Because it's still a privately owned company, only small amounts of Facebook stock can be purchased by an exclusive club of Goldman Sachs' best buddies. That's

Because it's still a privately owned company, only small amounts of Facebook stock can be purchased by an exclusive club of Goldman Sachs' best buddies. That's the only reason for the absurdly high valuation. If this stock begins trading at $70B there's nothing to stop every hedge fund in the world from short selling it into the ground. Wall Street was skeptical of Google too but they proved everyone wrong once the ad money started rolling in.