I was invited through SourceForge to take part in a study of Microfoundations and dynamics of online interactions and behavior. They repeated traditional experiments, but online. Eg. they grouped people into pairs and said that one of you gives an amount between \$0 and \$10, and the other one receives 3x that amount, but then has to choose an amount to give back. It's real money, and you get it paid into your Paypal account at the end. There were 4 games, and you receive your earnings from a random one of them, plus a guaranteed \$10. Unfortunately I earned \$0 in the game that was picked (random:-)).