I will be upgrading from my 2006 17" MacBook Pro to the 13.3" MacBook Air. Though I'm puzzled why Apple opted to go with USB 2.0 instead of the faster USB 3.0. The latter of which is faster than firewire. I'm also confused why Apple opted to make FaceTime a separate app instead of including it in iChatAV. One app active is better than keeping both active.
The FaceTime service does run in the background, listening for incoming calls even when the app is closed. You DO have to manually launch it to initiate a call, but unlike I'M, at least you don't have to keep it open and broad sat that you are online.
Ultimately, it feels more like a module for something bigger that apple is testing. I fully expect that FaceTime will be fully integrated into programs like Mail and Address Book and iLife so you can initiate from any program and not just video chat, but share content as well much like you currently do with iChat.
My understanding is that iChat video uses either Bonjour or AOL's relay servers depending on where on the network or Internet your party is, but FaceTime looks to be a protocol of its own; maybe it's Apple's way of bringing more functionality under its own roof as opposed to relying on a 3rd party (like AIM relay servers).