For general use, vista dosent do much that XP cant, and therefore for most people, upgrading is pointless unless you buy a new PC, in which case you dont really get a choice.

Im in the process of building a new system and so have bought vista ultimate x64, purely for DX10 and extra system memory support to feed my high def gaming habbit lol

however, it will run alongside XP untill the issues are fully ironed out.