I installed the x64 version (though I haven't played with it much yet). Creative's driver support currently sucks for Vista (either 32-bit or 64-bit), and my HDTV tuner won't ever have drivers, just like it doesn't have any for WinXP x64. But besides those, ATI's beta drivers actually seem to be pretty good for this stage, from what I've seen so far. Performance is quite good too, even with all the new GUI stuff. I haven't gotten a chance to install much software on it yet, but I don't anticipate running into too many problems.
Probably the main consideration is what hardware you have, and then seeing if drivers are available. If you have something important that isn't supported (like my HDTV tuner, in my case), you'll likely only end up using Vista for a few minutes each time until you want to boot back into your "real" OS to have all your devices working 😛
Also, keep in mind that the x64 version will not let you use unsigned device drivers, unless you select a boot-time option (F8) to allow them each time you boot your computer. I have to do this every time I boot to get sound from Creative's 6-month-old Vista beta drivers, since apparently they weren't signed.
