I upgraded to Vista recently, I can't really say my experience has been neither negative nor positive.
I mostly upgraded because I've had a disc laying around for a while, and got bored while I was home from work due to being sick.
It's still Windows, applications seem to work as I expect them to.
My hardware works fine, Asus P5W DH Dlx, C2D, X-Fi, 8800GTX, nothing exotic, so I guess that's to be expected(aside from the X-Fi, I never expect Creative stuff to work, new OS or not).
Stuff has moved around a lot, that confused me at first, but I'm getting familiar with it as I go.
Performance is about the same I'd say, slightly slower to boot, slightly faster to open applications, pre caching at work I'd guess.
UAC is incredibly annoying, so I turned it off, Security Center as well, no biggie, they didn't hide the options for that in some obscure place, so I file that under regular fresh-install-tweaking.
The one thing that...bothers(?) me is the memory usage.
It uses absolutely absurd amounts of memory on a fresh boot, problem being, I'm not in any way qualified to profile memory usage under Windows, so I don't really know how much is disk cache, RSS, etc etc.
Haven't run into memory issues so far though, so for now I just don't care.
In the end, Vista gets a score of "whatever" from me, nothing new for me, but no major complaints either.
It works, so did XP, if I bought a new computer, I'd take Vista, but I won't be upgrading any of my other computers until I really need to.
It needs to be said though, I'm one of those people that thinks everything was better "back then".
I don't like changes, and I generally leave new features of stuff unused for a long time unless it was something I was actually waiting for.
Depending on what type of user you are, I'm sure you could benefit a lot more than me from Vista, or it could be complete crap.