There's two reasons why I won't get Vista. Right now, with the release of SP1, it has gotten better from my understanding. I'll be waiting for SP2 to come out before I get Vista, until then I'll stick with XP SP3.
Reason why is software compatibility. Some of the software I use I think are not Vista compatible, I'd have to verify.
Another reason is RAM. I have 4 gigs of ram and I do have a gaming machine, well, I will in a few hours after I get it built. Down the line I plan to upgrade to 8 gigs, but for now, 4 is sufficient. Crysis needs 1 GB with XP and 2 GB with Vista. I know I won't see the full 4 gigs with XP, but with Vista it does require more ram.
I don't really have a use or advantage right now really, but I wouldn't mind using Vista. It is a bunch more secure than XP, that's for sure. I might load Vista onto another HDD that I have and run it to compare the difference with XP. I'll probably even load a fresh copy of XP to make it a more reliable and valid comparison. I just don't know if I should go with 64 bit since I have to verify some of my compatibilities.