Correct me if I'm wrong, but it looks like you're using (rumored) 2009 income numbers with the Jan. 2011 valuation in your calculation. Income surely would have changed since then.
Yes, that's true. Assuming 2009's valuation of 25 billion, that would mean a P:E ration of 125:1.
You're comparing their 2010 year-end valuation with their 2009 year-end net income...
In December 2009, Facebook repurchased shares at $25 for an implied valuation of $11 billion. That's a 55 P/E.