The only trouble I had was that my 64bit laptop somehow installed the 32 bit version leaving me with a gig of ram that I couldn't use. The "Anytime Upgrade" doesn't allow you to swap from 32 to 64bit. In the end, I had to use my vista restore disk, reinstall Vista then run the upgrade disc again this time weeding through the folders to make sure I myself ran the 64bit update. Did a clean install, and got it to work.

Since that little hiccup, 7 64bit has run flawlessly. 32bit did also, but I need my ram! Others I'm heard of doing the install over Vista say it works pretty well, but that it's a little slower then they expected. Hope this helps!