It's done it twice so far, once yesterday when the dock also became unresponsive, only a hard reboot would fixe the issue, I couldn't even use the apple menu to restart the computer. Just now hot corners have stopped working completely. The only difference from 5 minutes ago is that I disconnected my external display, and installed flash player 10.1 pre-release. Any suggestions? I'm using both the trackpad and a bluetooth might mouse, both do not trigger my hot corners. Edit: I plugged my external back in and unplugged it again, and now everything works. Odd.