The MacBook Air is so slim… mainly because it comes without a lot of things, besides an optical drive.
For one thing, the battery is ‘integrated’, meaning you can’t change it. No spare batteries for long flights or business trips. If you’re flying coach, spare batteries are handy – there’s no power jack in coach on most airlines (good excuse to fly business class). The magsafe connector is different, meaning you can’t use older magsafe power supplies.
There’s no Ethernet port (there is an inexpensive USB to Ethernet adapter). There’s no FireWire and only one USB port (looks like Apple is finally shooting FireWire). If you want a mouse and, say, the optical drive at the same time, you’re going to need a USB hub (and there might be power problems with that).
Apparently, you can’t add RAM, either. Photoshop, Aperture, Lightroom and Final Cut users may have issues with a ‘mere’ 2GB of RAM.
To be fair, every other ultralight makes trade offs. Apple’s choices may be good ones… we’ll just have to get one and see… (photos courtesy Apple Computer)