Well, I think the point is that Microsoft gave Facebook $240 million in exchange for a few things. A "strategic alliance", 1.6% equity stake, an advertising dea

Well, I think the point is that Microsoft gave Facebook $240 million in exchange for a few things. A "strategic alliance", 1.6% equity stake, an advertising deal for Facebook ads outside the US, etc. Now, it's not correct to just multiply those numbers to arrive at Facebook's book value, but the deal certainly values Facebook very highly: as a company that Microsoft is willing to essentially give $240 million to at a very generous valuation. So while Facebook aren't a $15 billion company, they're a company that can raise $240 million in exchange for a small equity slice and an ad deal -- which is a very highly-valued (overvalued?) company indeed.