One way to describe Facebook is as the most extensive data set on human social behavior that ever was. Every month more than 845 million people record and share traces of their daily lives, relationships, and online activity through their friend connections, messages, photos, check-ins, and clicks. The richness of that information goes some way to explain why the company is expected to become worth more than $80 billion when it floats on the stock market later this year…Read more here.