The new aluminum-clad MacBook Air, which I’ve been testing for several days, is billed as the world’s thinnest notebook computer. Its thickest point measures just three-quarters of an inch, which is slimmer than the thinnest point on some other subnotebooks. And it employs some innovative software features, such as fingertip gestures for its touchpad that are similar to those on Apple’s iPhone.

Apple refused to make the most common compromise computer makers employ to create their littlest laptops. Other subnotebooks — a category generally defined as weighing three pounds or less — have screens of just 10 to 12 inches and compressed keyboards. The three-pound MacBook Air, by contrast, features a 13.3-inch display and a full-size keyboard.

It’s impossible to convey in words just how pleasing and surprising this computer feels in the hand. It’s so svelte when closed that it’s a real shock to discover the big screen and keyboard inside.

But there’s a price for this laptop’s daring design: Apple had to give up some features road warriors consider standard in a subnotebook, and certain of these omissions are radical. Chief among them is the lack of a removable battery. So, while the MacBook Air will be a perfect choice for some travelers, I can’t recommend it for all. It really depends on your style of working on the road and what features you value most.

The MacBook Air, which will be available next week, costs $1,800 with an 80-gigabyte hard drive and a generous two gigabytes of memory. A second model, with a faster, cutting-edge, 64-gigabyte, solid-state drive and a slightly speedier processor, costs a whopping $3,100. The $1,800 price for the main model isn’t unusual in subnotebooks, which can easily top $2,000, although some competitors cost less.

In my tests, the MacBook Air’s screen and keyboard were a pleasure to use. The machine felt speedy, even with multiple programs running. And the laptop has the same Leopard operating system, superior built-in software, and paucity of viruses and spyware that I believe generally give the Mac an edge. I was able to install and run Windows XP using the third-party Parallels software.

But then there are those trade-offs. The sealed-in battery means you can’t carry a spare in case you run out of juice, and you have to bring it to a dealer when you need a new one. There’s no built-in DVD drive. The thin case can’t accommodate a larger internal hard disk. And the machine omits many common ports and connectors.

The MacBook Air

There’s no Ethernet jack for wired broadband Internet connections and no dedicated slot for the most common types of external cellphone modems. That means that out of the box, the MacBook Air has only one way to get on the Internet — through its fast, built-in Wi-Fi connection. If you’re out of Wi-Fi range, you’re out of luck, unless you buy an optional, $30 add-on Ethernet connector or a cellphone modem that connects via USB.

In fact, the MacBook Air has only three connectors: a headphone jack, a single USB port and a port for connecting an external monitor.

That single USB port is a problem, because so many peripherals use USB. You can buy a tiny, cheap USB hub that adds three more ports, but that’s yet another item to carry.

The lack of a DVD drive is partly solved by some clever software Apple included that lets you “borrow” the DVD drive on any other Mac or Windows PC on your network, so you can transfer files or install new software from a CD or DVD. This worked fine in my tests, in which I installed several new programs from CDs on remote computers, but it requires disabling third-party firewalls on Windows machines. It also doesn’t work for installing Windows on your Mac, for watching DVDs, or for playing or importing music. For those tasks, you need an external DVD drive. Apple sells one for $99.

In my standard battery test, where I disable all power-saving features, set the screen brightness at maximum, turn on the Wi-Fi and play an endless loop of music, the MacBook Air’s battery lasted 3 hours, 24 minutes. That means you could likely get 4.5 hours in a normal work pattern, almost the five hours Apple claims.

But the MacBook Air has another downside: its screen height. Because of the larger screen, the lid stands higher when opened than on most other subnotebooks. So it isn’t as usable as some competitors when the seat in front of you in coach on a plane is reclined.

If you value thinness, and a large screen and keyboard in a subnotebook, and don’t watch DVDs on planes or require spare batteries, the MacBook Air might be just the ticket. But if you rely on spare batteries, expect the usual array of ports, or like to play DVDs on planes, this isn’t the computer to buy.

• Email me at mossberg@wsj.com. Find all my columns and videos online, free, at the new All Things Digital Web site, http://walt.allthingsd.com.

But there’s a substantial minority of folks who have neither the time, knowledge, nor inclination to do all this downloading and ripping. They don’t want to fool around with any PC software just to hear music. They could just sign up for a subscription service like Rhapsody, which will stream songs to you without requiring any downloading or ripping. But that also has meant using a PC.

The Sonos controller, accessing the Rhapsody music service

Until now. Starting today, there’s a way to get access to Rhapsody’s 2.5 million digital tunes, in any room in your house, straight from the Internet — without even turning on your computer.

This new system is a time/money tradeoff. It saves you time (and what some folks consider a big hassle) in exchange for money: $999 for the basic hardware, plus $10 a month for the music service.

If you’re still reading after digesting those prices, let me add that I’ve been testing this system, which pairs up Rhapsody with the elegant Sonos whole-house music system, and it works very well. It is simple, fast and rewarding.

Both Sonos and Rhapsody were originally designed to work with PCs. Sonos is the most polished consumer hardware system on the market for taking the music that resides on a computer and streaming it to multiple other rooms of your home. It consists of a series of small music-playback boxes that connect to each other over their own wireless network. It normally relies on software you install on the computer. The system is controlled by a gorgeous hand-held remote with an iPod-like wheel and a large, bright color screen that show menus and song information.

Rhapsody, too, is typically dependent on a PC. Users pay a monthly fee to either “stream” music from its collection, or to download it for use on the computer or on a portable device. This is all done using Rhapsody’s software, or a Web browser.

But, with the new Sonos/Rhapsody system, no PC is necessary. You just connect the Sonos hardware to your Internet service, and to either powered speakers or an audio system. Then, simply click on the Rhapsody choice in the menu on the Sonos controller and you can listen to any of Rhapsody’s 2.5 million tracks.

Out of the box, the new Sonos system gives you a 30-day free trial to Rhapsody, without even requiring that you enter a credit card. After that, you must pay $10 a month.

There are other media-streaming devices that can bring Rhapsody to parts of a home far from the computer, and most cost less than Sonos. But all of them, even an earlier implementation using Sonos, require a PC.

Setup of Sonos with Rhapsody was simple. For your $999, you get two small Sonos ZP80 players and one controller. You plug one of the players into your home Internet router so it can fetch the music over the Internet from Rhapsody. The second unit can then be placed in a distant room, with speakers or an audio system, where you wish to hear the music. The two units are linked by their own wireless network, which sets itself up in a few minutes with the press of a couple of buttons.

You can even do this with a single Sonos box connected to the router or to an Ethernet cable running through your walls, if you have one. That would save you some money; a single ZP80 is $349 and the controller is $399, for a total of around $750.

Once you are set up, you just click on “Rhapsody Trial” on the Sonos controller, and you can then select songs via genre, artist and other criteria. Again, there are no files to download. Nothing gets stored on your computer or on the Sonos hardware. The music is just streamed into your home over the Internet.

There are two basic Rhapsody modes. One, called Rhapsody Guide, lets you find and play music, and allows you to “save” the songs or albums to your Rhapsody library. This is a list of songs that the system will fetch from the Rhapsody servers when you want to hear them again. The other, called Rhapsody Radio, consists of over 100 “radio stations” — preprogrammed playlists — based on genres, eras and other criteria. You can also create your own stations.

Although my wife and I aren’t great candidates for this product, because we use iPods and iTunes and have a computer hooked up to our entertainment system, we both got a kick out of the Sonos/Rhapsody package. I found myself scrolling through old rock ‘n’ roll on the treadmill, and she enjoyed a radio station of Broadway show tunes.

There are some drawbacks. Because of complex music-industry policies, a small percentage of songs can’t be streamed, yet they still show up in Rhapsody’s menus, which leads to frustration. And Sonos hasn’t been able to implement a search feature yet, which leaves you doing a lot of scrolling through menus.

But, overall, this is a very good digital-music alternative for people with a roomy budget and a yen for simplicity.

Write to Walter S. Mossberg at mossberg@wsj.com

But there’s more than one way to get a strong, fast Internet signal all over your house. You aren’t limited to using a single wireless router. You don’t have to install a bunch of complicated wireless “range extenders.” And you don’t have to snake networking cables through your walls.

Instead, there’s a simple alternative that’s often overlooked: Using small gadgets called Powerline adapters, you can route your Internet connection around your house over your regular electrical power lines, the ones already in your walls. It really works, it’s fast and it doesn’t disrupt your electrical system. Even better, it requires zero technical skill.

You just plug one of the adapters into a standard electrical outlet near the place where your Internet connection enters your home. Then, you connect the adapter to your wired or wireless router. Next, you plug a second, identical adapter into an electrical outlet in a distant room where you lack an Internet connection. Finally, you plug a computer (or even a wireless access point) into that second adapter. There’s no setup, no required software and no technicians or tools are needed.

When you plug in a computer into the second Powerline adapter, it’s as if that computer was right next to your cable or DSL modem and router. You are on the Internet at full speed. If you plug a Wi-Fi wireless access point into the second Powerline adapter, it will create a wireless network in and around the distant room, which multiple computers can use.

I first reviewed these Powerline adapters in 2003. I liked them, but they were a little slow and never took off. Now, however, one of the leading home network product makers, Netgear, offers a whole line of faster Powerline adapters.

I’ve been testing one of Netgear’s newest models, the XE104, which costs $100 per adapter, and I can heartily recommend it. It couldn’t be simpler or more effective. In my tests, the XE104 gave me wicked-fast connections. I tried plugging Windows and Macintosh laptops directly into the adapters in rooms where my wireless signal was weakest. I also tried plugging a Wi-Fi wireless access point into an XE104 adapter and picking up the connection wirelessly on the laptops. (An access point is a wireless gadget that takes a wired Internet connection and propagates it through the air.)

In all scenarios, the Netgear XE104 adapters delivered nearly the full speed of my Internet service, which in my case is very fast — 15 megabits per second downstream and two mbps upstream. In fact, the XE104 can handle speeds up to 85 mbps, far faster than any common connection.

You can use up to four Netgear adapters at once, and the company claims they will cover a 5,000-square-foot home. Netgear includes optional software to encrypt your Powerline connection, but this is needed only if you share an electrical system with other families.

Linksys, Belkin and other companies also make Powerline adapters, sometimes called bridges. But Netgear is the leader in this category, and I didn’t test the other brands.

The XE104 is a small, white rectangular gadget about 4 inches high, 3 inches wide and 1.5 inches thick. It carries a standard two-pronged electrical plug and mounts right into the wall outlet.

On the side, there are four standard Ethernet network ports, like the kind on your router and laptop. Netgear includes a short Ethernet cable so you can connect the first adapter to your router and the second one to a PC or a wireless access point.

The four Ethernet ports are what make the XE104 a “switch.” They allow you to connect each adapter to multiple devices. For instance, the first adapter can be connected both to your router and to a PC. The second might be connected to a PC, a wireless access point and a device like a game console.

Netgear makes a similar model without the multiple Ethernet ports, called the XE103, for $80. There’s also a costlier model that goes up to 200 mbps, though that’s overkill for 99% of people.

The company also makes a Powerline adapter with a built-in wireless access point for the distant room, the $150 WGXB102 model. This saves you the cost and hassle of buying and connecting a separate access point. But it’s slower and uses older technology. In my tests, it was less than half as fast as using the XE104 with a separate, modern wireless access point.

Unfortunately, like a lot of network-equipment makers, Netgear is clueless about naming products so that normal humans can understand what they are. The XE104 is officially called the XE104 85 Mbps Wall-Plugged Ethernet Switch. That’s like calling a table lamp the LS482 75 Watt Wall-Plugged Switched Illumination Device.

Netgear even makes it hard to find the XE104 on its Web site, netgear.com. It lists it under a section called “Bridges, Access Points, and Range Extenders.” You can buy them at computer stores and other retail outlets.

These adapters are a terrific way to clear up Internet dead spots.

• Email me at mossberg@wsj.com.

Apple and Sony are the usual suspects. Microsoft and Intel, which dominate the industry, rarely make the list of design risk-takers. So the latter two leaders deserve credit for cooking up a whole new type of Windows computer — a machine that’s smaller than the smallest mainstream laptop — the Ultra Mobile PC, or UMPC. The first UMPC for the U.S. market, the Samsung Q1, goes on sale next week at Best Buy’s Web site.

The idea behind the UMPC is that it’s so small, yet so full-featured, it can replace a laptop. It’s meant to fit in places a laptop won’t, or simply to be held in your hands. It is also supposed to be a cool multimedia device for watching video or listening to music.

Unfortunately, the Samsung Q1 is so deeply flawed in key respects that it amounts to little more than a toy for techies. For everyone else, it’s impractical and frustrating. Unless the UMPC can evolve significantly beyond this first effort, it may wind up as a footnote in the history of personal computers, rather than an exciting new category.

The Q1 is sleek and attractive. It’s about the size of a hardcover book, only narrower, and is clad in shiny black plastic with silver accents. Most of the unit is occupied by a wide-angle color touch screen that measures 7 inches diagonally. Overall, it’s about 9 inches long, 5.5 inches wide and just under an inch thick. It weighs a scant 1.7 pounds.

Inside, the little machine runs a full version of the Tablet edition of Windows XP. In fact, the UMPC, which Microsoft had code-named Origami, is really just a small Tablet PC. That’s a good thing, because many of the Tablets shipped so far have been too big and bulky to use comfortably as electronic notepads or document readers, which are the main functions of tablet computers.

The Q1 uses a slow, low-end Intel processor, a Celeron running at 900 megahertz. But it was adequate for the common tasks I tested — Web surfing, email, playback of audio and video files. There’s also a 40 gigabyte hard disk, 512 megabytes of memory, Wi-Fi and Bluetooth wireless networking, an Ethernet port, two USB ports and a slot for Compact Flash memory cards.

There’s no embedded cellphone modem and no slot for adding an external one. The Q1 also lacks an internal DVD drive. An external drive can be added for $219, but it’s an extra piece to carry and plug in.

You operate the Q1 like a PDA — by manipulating icons on the screen and writing on the screen using either a simple plastic stylus or your fingers. It lacks a built-in keyboard and doesn’t come with a mouse.

In my tests, the Wi-Fi and wired networking worked well and were fast. All the applications I tried launched fine and worked fine. Video clips looked pretty good on the screen, and the stereo speakers, though small, did a decent job.

So what are the Q1’s big flaws? The first is price. Microsoft’s designers set a target retail price of $500, but Samsung is charging more than double that amount — $1,099. That’s more than many laptops cost, and much more than PDAs or smart phones. In fairness, the lightest laptops tend to cost more — $1,500 to $2,500. But $1,099 is still a lot for a UMPC.

The second is battery life. In my harsh battery test, the Q1 lasted just two hours and two minutes. That means that, in normal use, it might approach three hours, if you’re lucky. You can buy a larger battery for $119, but it adds bulk to the computer and nudges the weight up to two pounds, almost as heavy as the lightest standard laptops.

The third is the lack of a keyboard. Without a keyboard, many standard tasks in Windows are simply a huge hassle. You can’t really do word processing at speeds most people are used to. And email is a constant frustration. Yes, the Q1 has handwriting recognition, but it’s cumbersome. And there’s a semicircular onscreen keyboard, but it takes work to use it well.

Most Tablet PCs include a keyboard. Even the tiny OQO computer has a keyboard, as do Treos and BlackBerrys. How come the combined brains at Microsoft, Intel and Samsung couldn’t build one into the Q1? You can plug in an external keyboard, but that makes the machine ungainly.

The fourth big flaw is the screen. Its resolution is too low to see much material at a glance. Often, you can’t even see the OK button at the bottom of open Windows. There is a way to increase the resolution, but it results in distorted graphics and fuzzy text.

Finally, the navigation buttons and controls on the Q1 are awful. There’s a control that moves the cursor, and another that acts like a Return key. But there are no direct equivalents of the left and right mouse buttons. To emulate a mouse button, you have to hold down two of the Q1 buttons simultaneously.

My advice is to skip the Q1, and hope that the next generation of the UMPC will be better.

• Email me at mossberg@wsj.com.