If I pay $250,000 for 1% of an offshore well, that does not value the well at $25,000,000. In fact, my 1% is completely worthless if oil/gas is not struck. Same goes for Facebook, the userbase is the oil. Until they are traded on an OPEN market, the value is still anybody's guess, no matter what Goldman or Microsoft or whoever offers. What Facebook amounts to is a very large "pile of eyes", and as has already been proven on the internet, those piles can dissipate very quickly.
The CEO is supposedly worth more than the companies all time cumulative revenue.
As long as the #1 search term is "facebook" and the #2 is "facebook login", Google doesn't have to compete with Facebook as they are already the layer around it.