Comment 81 for bug 762918

I also get the screen freeze often at the screensaver
This has worked for me more than once:
  I go into Ctrl+Alt+F6 and login,
  View processes as tree with e.g. sudo htop,
  Find compiz processes under which are the unity window decorator and such
  Kill it and go back to Ctrl+Alt+F7

Windows will reappear as they were left, and a surprising improvement in the windows animations!

I hope this works for you guys too.