I use windows 7 both in my home PC, and work laptop, and it is good enough that I am building a desktop PC in 7 to replace my XP machine.
Windows 7 uses hardware acelaration for the desktop. Vista was all CPU bound. that is what made XP faster.
Also, IMHO it has a much, much improved memory management and program isolation than XP and Vista. Vista is good at isolating programs, but the memory management wasn't as good as 7.
Overral it feels faster than XP and Vista, however once you start putting programs I think it is the same. It is not a must upgrade, but if you are looking to upgrade then there is absolutely no reason not to go with Windows 7. If I was given the option of XP or Vista, I chose XP, XP or 7 I chose 7.