I'VE GOT THE ANSWER!!!
Did you just install Panther? Do you have Synergy installed? If you do you need to update. For some reason it becomes a hot key for Synergy when you update to panther. Since Synergy begins at start up you never notice it coming on. Delete synergy from the Preference Pane menu and restart. If this doesn't apply, make sure you don't have any other programs running hot keys. This happened on 4 of my friends computers before we figured it out.