I love vista and it is very fast on my laptop...granted I do not have a bunch of programs installed other the the default ones and, photoshop cs, firefox, putty, miofactory, norton anti-virus, and a scientific calculator that I have not used since my general chemistry days...
If you are looking for a reason to upgrade then you will find that there are not all that many reasons to do so, I would take Boofo's avice on this issue. Or you could listen to nex and get a mac...I bet vista would not slow a
mac down...