DirectX 10, Support for Robson(fast boot times on laptops soon) and others.
Latest from Ars Technica, who called Microsoft (duh, whoda thunk of that?), says basically that Vista has a hardware-change algorithm just like XP had, although apparently a bit smarter.
If it triggers (say you put in a new mobo), it will still run, counting as one transfer. You will have to call Microsoft support to keep running if you trigger it again, but reports say MS support is has been pretty lenient about that in the past with XP. Previously the general number of reactivations allowed through support was 10, but Microsoft isn't saying how many this time.