Not for playing around with

Go here and play Google Image Labeler, and I guarantee your life will be ruined, all your plans will come to nothing, your partner and your family will ultimately abandon you, you'll lose your job and you'll die prematurely, alone and in great sorrow.

On the other hand, it is bloody good fun. I'm on 3320.

Only thing is, you don't get to choose who to play against. Some people are reaaaally dumb.