From Carnegie Mellon:
When you play a game at Gwap, you aren't just having fun. You're helping the world become a better place. By playing our games, you're training computers to solve problems for humans all over the world. Take the ESP Game for example. You and a partner see the same image and are asked to type in a tag for it. When you agree on a tag, you move on and are awarded points. After just a minute of play, you've agreed on six or seven tags. We record those six or seven tags and associate them with the images. Now a search engine will have a better idea of what's in those images. Everyone benefits.