Just upgraded my work workstation (as opposed to home workstation) to Windows 7 Professional 64 bit. Did an in-place upgrade from Vista 7 Business 64 bit.
So far no problems. I still had to turn off UAC, but that was a lot easier than before. Only hiccup so far was that the upgrade removed the VirtualBox driver that allowed my guest OS to connect to the network. Upgrading to 3.0.4 from 3.0.2 resolved that.
Only took about an hour and a half to complete the upgrade, which was very nice.
Initial impressions are favourable. We'll see if any major glitches or annoyances crop up.