I'm sad to report my first installation problem with Windows 7 since 6801. Yesterday I tried to upgrade 7100 to 7201 (x64). I got some incompatibility reports for a few applications (ATI Control Center, ATI Software Installer, Daemon TOOLS), but I carried on with the upgrade without removing these apps first. Guess what - "Upgrade has been cancelled" message after about half an hour, and "Restoring to previous state" (or summit like that). However, restore apparently did not work either, I'm now having all sorts of problems (Windows Installer Service giving Access Denied, various apps not working...), so will have to reinstall from clean.
I guess it pays to follow the installer recommendations ;-) Still, I'm sorry to see that the upgrade procedure is not exactly bulletproof.