everyone's mad they didn't think of it first. it's the most brilliant scam I've ever encountered, doubly so because you can make the case that it's not technically a scam.
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 :)
(For the record, I don't think it's a terrible thing or should be illegal, no matter how profitable.)