1) Is the MacAir suitable as your "real" computer? No.
OK: that's a spoiled-sounding thing to say. What I mean is that this machine is optimized for ease, convenience, and elegance as a portable computer, at the expense of features that would make it better for day-in, day-out stuck at the office use.
Most obvious illustration: this is one of the very few modern computers with no CD/DVD drive at all. (Unlike its closest PC counterpart, the new Lenovo ThinkPad X300.) You can work around that with a convenient utility to read from another machine's DVD drive, over a network -- but that means you have to have another machine. Similarly: you can work around the absence of an Ethernet port (with a separate dongle), and the presence of only one USB port, and the absence of a microphone jack. But they are workarounds, and there is no getting around the limit on the hard drive, which holds a maximum of 80GB. Not a huge amount, by today's desktop computer standards.
The MacAir remains elegant and beautiful; it has stood up well to travel (protected by this neoprene sleeve); I have no complaints about fit or finish or any other mechanical feature. But just as some resort properties are suitable mainly for those who can consider them "second homes," this is suitable mainly for people who can consider it a second computer. Though a nice one....
2) What about that battery life?
It seems to have settled out at three-plus hours of real, dependable working time. That's roughly what I get from one of my ThinkPad T60 batteries -- the difference being that I can take extra TP batteries and swap them during a long flight. The MacAir's battery, like the iPod's, is not supposed to be swappable except at the factory.
But here is an expensive but effective workaround, first suggested to me by Edward Goldstick. The QuickerTek company, of Wichita, Kansas, makes an external ~$300 battery charger that is claimed to provide six to ten additional hours of usable battery life. I decided to get one before a recent 13 hour flight back to Beijing -- and while I didn't work every minute of that flight, there still was plenty of extra juice left when I had to shut down the computer for landing. (It was running for at least eight hours.) The charging device itself is either ugly or industrially-chic, depending how you feel minute by minute. It's a burnished metal square, roughly 5" x 5" and half an inch thick, weighing just over a pound. You connect it to the MacAir and it provides roughly as much working time as two spare batteries do for the ThinkPad. The only real drawback is that it's another thing to be attached to the laptop, rather than fitting inside. Worth at least checking out -- and the cost is not that much more than two additional ThinkPad batteries would be.
3) What about that keyboard?
I don't think I'll ever like the Mac keyboard layout as much as I love the arrangement and feel of ThinkPad keyboards. But I have come to like one Mac feature well enough to miss it on my ThinkPad: "two-finger scroll," which lets you put two fingers on the touchpad and then move up and down through web pages, documents, anything. And I am learning the workarounds for the Mac's various keyboard oddities (no DEL key, different function for F5 and similar F keys, and on down the familiar list) to be less actively bothered by them. Crucially, the keyboard feel on the MacBook Air is good. Apart from two-finger scroll, the Mac keyboard will never be a plus for me; but it's less of a minus.
Some other day, some other three-point list.