Ars Technica has a pretty good review of the Apple Air and its strong and weak points. For me, the things that don’t work, out weight those that do.
For example, it can’t be used as a primary PC unless you buy the accessory external optical drive and maybe the external Ethernet dongle. Otherwise, getting data into and out of it with WiFi may be problematic.
Secondly, the hard drive is too slow. Whenever any background task occurs, the foreground task may stop. This is the deal breaker for me because I need a business class laptop that can be used for presentations that include displaying video. Said videos must smoothly play while I also run other programs in background, such as a word processor where my notes may be and/or a spreadsheet where my numbers may be. Hence, anytime the hard drive is accessed could cause the playback to stutter or pause. This is just not acceptable. Hence, until Apple includes a faster drive (and faster processor) this won’t work for me.
The review also notes the short battery life (a little over two hours) but that doesn’t matter to me because I would always be tied to A/C.
Still, if the Air is not your primary PC and you can live with stutters and stops as you surf the web (and don’t mind paying hundreds more for an Apple than [insert name here]), Apple’s latest laptop might work for you. YMMV. Insert disclaimer here.