A recent reshuffle of Facebook shares on SecondMarket indicates that share prices have surpassed the $20 mark.
With 2.5 billion outstanding shares Facebook's valuation works out to around $50 billion, the highest valuation for a private company yet. In terms of value Facebook has already surpassed Yahoo and Ebay, not to mention other social networking sites. This is rather impressive for a six year old company.
It is unclear whether Facebook is planning to go public at any point in the future. It would make for a rather interesting IPO though.