The MacBook Air has no optical drive, no Ethernet, only one USB port, small hard drive and measly processor - you know the story by now. So you're paying a massive premium to sacrifice all these features so you can slim down by less than a centimetre and shed less than a kilo. For most users I'd say it's too big a sacrifice to make.
The high-end MacBooks run rings around the MacBook Air in terms of performance. Right now I've got a 1.6 GHz MacBook Air sitting next to a 2.2 GHz MacBook (both with 2 GB of RAM). Naturally the MacBook thumps the MacBook Air when it comes to benchmarks, boot times and responsiveness. More surprisingly, the MacBook also outlasted the MacBook Air by 45 minutes in my light-use battery tests. Another strike against the waffer thin MacBook Air.
Now Apple has beefed up the MacBook and MacBook Pro, while trimming the price, it's even harder to justify splashing out the MacBook Air. Talking in US greenbacks, the entry level MacBook is now $700 ($AU1000) cheaper than the entry level MacBook Air. For the 1.6 Ghz MacBook Air's $1799 ($AU2499) price tag you can get the new top of the line black MacBook which features a 2.4 GHz processor, 2 GB of RAM standard and a 250 GB hard disk drive - plus a heap of features that are missing from the MacBook Air. You'd still have a few hundred dollars left over to put towards the AppleCare Protection Plan for extended support and warranty.
The MacBook Air has its place, but that place is as your secondary on-the-road companion rather than your primary everyday workhorse. It might be a good luxury item for the Apple faithful who already have a Mac or two lying around, but everyone else should think carefully before taking the leap into thin air.