Apple announced the new MacBook Air this week, and as of today, they appeared in my nearest (albeit not quite local, per se) Apple Store. As someone long fascinated by the MBA, and who also will be upgrading his 2-year-old 15-inch MacBook Pro in January, I decided to have a look.

The new Air comes in an 11- and 13-inch version, and as I walked into the store, it was the smaller one that happened to be available, so I sidled up and started to play. I was immediately struck by how small it is. The physical size, of course, but also the display resolution. You don’t really get a sense of how diminutive the Air is until you close it and hold it in your hand. This machine is a veritable sliver of aluminum.

It was very snappy to use. Apps opened right away, responsiveness was quite excellent, no doubt owing to the flash memory. I played 1080p video from Apple’s trailers site, and it used about 45% of the CPU; the machine barely got warm. Flash video was a different story: on I watched a 720p video stutter occasionally, and the CPU took 150% between Flash and Safari. In other words, it was exactly as you would expect on a Mac.

I opened the brand-new Word 2011, and it was available almost immediately. I have the previous version myself, and I dread using it because I don’t want to wait for it to start. This was a real revelation. But once open, you can see that the app is kind of a joke on a screen of this size. With the Dock visible at the bottom of the screen, and that grotesque Microsoft Ribbon taking up a ton of vertical space at the top, your document is a postage stamp in the middle. If you switch the view to Draft mode, and hide the Ribbon, it becomes much more usable.

On the other hand, I downloaded and installed Coda, Transmit, and played with Photoshop Elements. You know what? They look pretty darned good on that screen, and worked without compromise.

The 11-incher has a resolution of 1366×768 — the first 16:9 display I believe Apple has produced. Despite most apps working well, I think you really feel cramped with such a short display.

But when I closed that MacBook Air and held it in my hand, it was wonderfully compelling. All that computing power in such a slim, svelte package.

The 13-inch Air was much more convincing as a primary computer. It has more oomph than the smaller one, but its display resolution is a delightfully uncompromising 1440×900 — exactly the same as my current 15-inch MacBook Pro. Of course, the high resolution of this display means that everything on the screen is smaller. My eyes aren’t getting any younger, but they’re still good enough to read it comfortably. But shortly after, looking at their 15-inch MacBook for comparison, I was shocked — shocked! — at how big things looked on that display. It was a dramatic difference in size.

So what do I think of these machines? When Steve introduced them on Wednesday, he suggested that all their computers would be like this down the line, and I can see what he means: this form factor is clearly the future of portable computing. The 15-incher (and definitely the 17-incher) look clunky, bulky and archaic.

We have always been asked to give up power for portability, and the equation remains unchanged. But today’s less-powerful computers are probably more than enough for most users. I’m certain that my Mom could probably get by with an iPad; my wife could easily get by with an Air; but could I?

Putting on my Vulcan hat for a second: In my objective analysis, the 11-inch display is simply too short, and I would probably chafe against that repeatedly. The performance on it was quite brilliant, but I would like to see some metrics from reviewers such as Macworld.

The 13-inch model was very, very compelling. For just a bit larger than the 11-inch model, you get a display that I already know I’m comfortable with in terms of pixel resolution. It comes with a faster processor, and critically, the larger flash capacity (256GB in the upgraded model).

On paper, trading in my 15-inch MacBook Pro for a 13-inch Air would seem ridiculous; the specs suggest I would be losing performance. But raw performance isn’t really an issue anymore; computers are “fast enough” for so many of the things we do with them. What you get instead, with the Air, is a feeling of absolute portability, the sense that it could effortlessly slip into any place you need to use it. It shifts the power of computing into the space that an iPad or netbook would occupy. I could take an Air to my coffee shop, and it would be so much easier to handle.

And yet, I could bring that Air back home with me, plug it into my 24-inch Cinema Display, and still get an uncompromising desktop experience.

So it’s definitely a conundrum. Luckily, I have a couple months to make up my mind!