Since I started using Natty I experience a strange situation at times. When I leave my system idle for 30+ mins., the screensaver Ant Spotlight remains active for specified time, then the monitor turns off after a while. Later when I am back to work on moving mouse/pressing keys on keyboard monitor powers on but I am greeted with a stuck up Ant in the screen. I won't be able to access open applications in any way. No key/mouse click works. I tried going to terminal with Ctrl+Alt+F1 and killing gnome-screensav but the Ant doesn't budge. Only way out I take is to log out with Ctrl+Alt+Backspace which works causing to lose my unsaved work.
I have the same problem on mine... does the same thing with GLMatrix.
At first I thought the problem was maybe due to using encrypted home directory, and since that was causing me grief in other ways I re-installed sans encryption. Still have the same problem.
Only fix so far that I've found is to turn off the screensaver.