Is a bubble coming? Well, is a valuation something passably sophisticated -- or is it a version of "Facebook has 500 million users... how much is a user worth?...oh, say, 100 bucks... presto, $50 billion!"
Maybe Google's IPO idea of "e * appropriate power of 10" lends a false air of accuracy -- all those digits! Not pulled out of thin air either.
PS. Ads? What ads? Facebook has ads?!?
Diplomacy is the art of saying "nice doggy" until you can find a rock.