I upgraded my new quad core machine to Vista 64 last month.

If you back up your /interface and /wtf directories and then reinstall, all will go smoothly. The 20 minutes that it takes to reinstall was worth the time spent. Wow will go in the /program files (x86) directory and will link in a bit differently. A couple of my programs did not reinstall well.

Norton Anti-virus (corporate edition)
Adobe Acrobat Pro (version 7) << still thinking about the upgrade $$ here, not sure it is worth maintaining this at home.
Keyclone (for some reason it didnt know i was on the same machine, i am impatient so i paid for another copy) + i own 6 copies now but i am using only two at the moment.

Overall, i am happy with Vista 64. Only a couple of weird crashes in the last couple of weeks. The ones where you get the screen to send data to Blizzard.

Good luck with the transition.

Sojolly