My cat got my gf locked out of Gmail for 15 minutes once, since it was sitting on the F5 (refresh) key while the Gmail tab was open. Turns out Gmail thought there was a suspicious activity on the account and she got locked out for up to 24 hours.
Fun times... at one point I managed to render a computer unresponsive by dropping a notebook on the PrintScreen key. The key-repeat was pretty fast and so many gnome-screenshot windows popped up...
Awesome. I find that simply lowering the screen when you get up works, except for when your cat is trying to express her affection to you or your screen while you're trying to get some work done.
Possible solution: http://i.stack.imgur.com/i1A5X.jpg