If I try to logout or switch user, I end up with a black screen and a blinking cursor. I can type and the letters show up on the screen but don't do anything. I can do Ctrl-Alt-F1 and then "sudo service kdm restart", but I'd rather fix the underlying problem...
Google gives several pages with similar problems but they all seem pretty old (2007), and they don't seem to apply to 10.10.
Any idea ?