Comment 20 for bug 181065

I've had this occasionally with Jaunty, including just now. gnome-screensaver was taking up 99% of CPU while it 'checked my password'. Killing gnome-screensaver didn't work - the X window didn't redraw itself, but just stayed stuck on a black screen with a white box where the 'Checking your password' window used to be. I had to reboot.

I had also just enabled automatic user login and then disabled it, similarly to what chrism2671 noted.