I had an idea for a non-evil gambling site a while back - basically runs at a profit with a small bias against the house. Not a scam, but it has a 'compelling mechanic' component in common with Swoopo (albeit a different mechanic).

On one hand I think it could make some cash while not being as dodgy as a regular gambling site, but on the other hand I don't want to encourage gambling addicts with the positive feedback.

I'm just glad it's not my only money-spinning idea :)