I have an 2 year old (fast) XP machine (mainly for serving files), and a new, moderate-spec laptop (for on the go), and a quite new Vista Desktop (for design and such).
I can honestly say, for now, Vista is not worth the hype nor the upgrade; its just a slower version of XP (yeah, eye-candy, but you can do that with apps anyway), with a few features, that you probably wont actually ever use.
The main problem is Aero and transparency, I think, once you disable that, Vista runs at reasonable speed. Wait until SP1, which should clear up some preformance issues.
I must say, some of the 'viewpoints' are terrably inaccurate, like those who said you need 4gb of ram to run Vista - that is utter bull. I can run Vista easily on 2gb (turning off an extra 2gb) of ram on my desktop, but it is very CPU intensive.
That being said, 4gb is excessive.