Google playing angles to make Facebook deal?

Sergey Brin was spotted having dinner with an associate from Greylock that is said to be involved in that company's Facebook investment. The meeting seemed to be important and rushed enough to hold just hours before Google's Q3 earnings conference call yesterday.

Rumors of a hot deal-making session were quickly dissolved by people who were actually at the dinner table, but it is still interesting to see that particular mix of people together -- even if it turns out to be a false alarm. Would a Facebook acquisition actually make sense for Google though?

A $15 billion investment (even for Google) is a giant lump of cash, but if they want to corner the North American social network market like they have with Orkut in Brazil, they need to spend cash. The question is, are social networks that valuable? Take the price tag divided by the number of users on Facebook (over 48 million according to Facebook) and you will see that an investment of $15 billion translates into $312 per registered user.

That is a lot of money -- can it be justified? If you had $200 billion in cash, would you be willing to drop 15 of that on Facebook?