Seems too easy to override, I tried the gmail "take a break" lab feature that locks you out of gmail for 15 minutes... but then I accidentally clicked it, and it was so easy to override with firebug (just delete the div covering everything) that it doesn't really do anything since I know its so easy to get around.

Maybe I will make one that you have to add a credit card too, and if it catches you it will draw $20 to a charity you hate. That might be a little more effective ;)