since my laptop is 32 bit CPU I can't run 64 bit on it, however, I had 64 bit Vista Ultimate run on my desk top, so far I had demo Crysis, Supreme Commnder, and play World of Warcraft, they all worked just fine. Only problems I had is Vongo not working after vongo did the upgrade on the client. but again vongo is a piece of sh*t company has poor programer, lying customer services, so I would not count on that.
I admitted I crash twice during play WoW when I have Dreamscreen as a back ground, after disable and just used normal back ground, it been rock stable.
there are alot of application didn't written for 64 bit, like Macro Media Flash player, 3Dmark 06, Adobe reader...etc, those will run in 32bit native mode. so far it just run and worked.
I think my hardware are far advance then Vista can handle, I am still try to find the way make all 8 core and 16GB ram scream