I have Windows 7 Enterprise (retail) installed on my MacBook, my work desktop (these two are 32-bit) and on my gaming rig (64 bit), and have been 100% happy. So far, no compatibility problems (although I've heard Batman Arkham Asylum has issues); basically, it's all the good stuff from Vista with the problems fixed (including "problems" that weren't problems, like UAC--it's much less intrusive in Vista). It's a faster OS, too, IMO--MS did a good job streamlining it (there's a version targeted specifically at netbooks, so the de-bloating shows.)