It makes sense, until you realize that Facebook does "Talent acquisitions" basically, i.e. with drop.io, friendster, etc.
He thinks highly of Adam for sure, but Adam also left Facebook to found Quora. I don't think Adam would want to be bought back by Facebook and actually stay there for any significant period of time.
Plus, there's Facebook Questions... (Of course, the quality of the questions/answers is certainly debatable)
I think one reason companies charge you the money immediately (for the "1 month trial") is to test out the credit card. I know some companies that charge a cent (or something) then refunds that to verify that the credit card is valid.