Sounds a bit silly, I don’t think a thief would take the time to log you off if they just wanted to swipe your laptop/tablet/UMPC : P

I think it would be funny to see someone unplug their computer forgetting that this software is installed, and have all eyes on them while they try to apologize for the annoying interruption.

Some more practical software like Lo-Jack for Laptops would probably be a better option, though its not free ; D