I finally got my hands on a MacBook Air. Though I'm sure I'm repeating what some others have said already, I needed to state one thing before I do a more extensive evaluation: this unbelievably thin notebook is rock solid.
NOTE: This is not an official CNET review. And is not by any means a full review. Just a quick first-look. Official CNET product review is here.
One of the concerns I had--and I'm sure I'm not alone--is whether a notebook this thin will be flimsy and overly delicate. The answer is a resounding no. It feels more solid in my hands than the rugged, well-built, 1.6-inch-thick HP Compaq nc8000 I have used for many years (since 2003).
The reason for this is the Air's aluminum construction and light weight. In other words, when you pick up the Air, you sense an almost perfect balance of sturdiness and weight--despite the fact that the Air exceeds the dimensions of a typical, more-compact subnotebook.
Update: One other quick impression. No excessive heat to speak of. Another challenge for designers of ultra-thin notebooks is how to effectively dissipate the heat that is generated by the core electronics, including the main processor, the graphics silicon, and hard drive. Apple has succeeded admirably. Admittedly, I am using the solid state drive (flash memory) version of the Air so there's no hard drive heat to worry about and I don't play games (some gamers have cited heat issues). Impressive nonetheless. More later.