I have Vista Ultimate and don't experience any of the problems listed by other people.
All games work fine, even older ones (except 16bits games under dos because I have Vista x64 which only runs 32 and 64 bits).
My computer runs faster with Vista then with XP pro, since XP pro can't handle all the resources my PC has to offer very well.
As for games made for Win xp I get like 5~10 frame loss, but when compatible directx 10 and Vista build they run faster then on win xp.
I never run UAC to start with, thats for the people who aren't able to protect and use their computer like it should anyways.
Also Vista Ultimate only uses 600Mb of ram and 1gb pagefile which is very low.
Vista doesn't start acting weird after running 3 weeks like xp does, in fact SP1 isn't out but it runs for about 1~2 months fine before acting weird (non stop, no reboot, ignore update reboots).
And lastly, Vista can deal with crap better then xp does, vga driver crash in xp = bsod and reboot, in Vista=relaunch vga driver and resume the job.
Vista, properly configured, with up to date drivers and a system that isn't strangling him but allow him to use all his potential, is better then xp.
If you want to know what I mean by properly configured just ask me.