So far I've been very impressed with Windows 7. It's really much lighter (it just uses 6GB of disk space and ran fine with a mere 512 MB), and for being a beta it seems very stable, the only thing worth reporting I found is Windows Defender being deactivated at random (mostly when I launch an Internet browser). The UAC is less annoying (I hope the new approach does not mean worse system security) than before, but it could be better (you don't have permission to view certain folders, you need to go through it whenever you want to check Defender's history), and generally most annoyances and idiosyncrasies of Vista disappeared or turned out for the better. It still needs lots of polish here and there (lacks consistence between different parts of the system), but it's shaping to be a really great OS. And FARR works! :)
Now, if I could find which folder is the new "My Documents" (Libraries or Users\<my name>), and how to move my entire profile (or at least the personal folders) all at once, instead of one by one...