I have a lot of experience w/ windows 7.
I have a laptop from 07 w/ vista and ran a clean install of XP and after much work with tweaking drivers, etc found no increase in performance, even though I had a lot more free resources.
Then a couple weeks later I installed windows 7 Release Candidate (test version) in the spring. It is awesome. My computer became much faster w/ 7 than it ever was w/ XP or Vista.
I ran a side by side test with a friends near identically spec'd dell (his is .2gHz faster, other than identical) and I was on firefox before he could even type his password to log on. I've had little to no driver issues, and I haven't had one blue screen, crash, or lockup.
It will be the new benchmark for sure!
PS: If you are a college student/have an .edu address you can get windows 7 professional for 30$(online download) or 30+13 for an actual disc. This is just an upgrade, you need a genuine windows copy of XP or Vista also.