There is one thing missing in most of the hype over Facebook's massive IPO. Everyone knows the company is popular, with 845 million users, and successful, with a potential valuation of $100 billion dollars. (That's five times the size of Google's 2004 debut.) But what exactly makes Facebook so valuable?

. Its users. Or more specifically, its users' stuff.

It is hard to measure how much of Facebook's value is derived by harvesting its user base. ...