I've been using 7 for approx 4 months now on a laptop I travel with, and use in my den at home. Probable average of 3 hours per day of use. Also due some heavy graphic design work on this computer. Have a total of 7 actively used computers at home by a variety of family members.
#1 complaint - I can no longer open multiple Firefox windows from the quick launch area of Windows. I have to go through a convoluted process of right clicking a bookmark link and open in new window. This is nuts!
#1 Compliment - Though the OS gradually seems to be taking over more of the computer, the system seems to be speeding up as a whole.
Another little gripe is why isn't One Care available for this OS. Don't you own the damn company? Are you going to refund me the months that I was unable to use it on this computer? - Although, I am really starting to like Avast...