The MacBook Air is an amazing piece of hardware. It's iPod sexy, but there's an iPod catch. Because just like an iPod, you can't just crack it open to replace the hard drive, memory or even battery, according to the Apple employees on the Macworld floor. Obviously a slew of services and devices will fill this battery replacement gap, but just know that when Apple pitches you 5 hours of runtime with the Air, that's all you get.
Update: AND THERE'S NO ETHERNET PORT EITHER!!!! -J.C.