Let's say that they have quadrupled that, so $3.2 B revenue, and that they have greatly reduced their operating expenses (new servers, etc.) - so let's say they

Let's say that they have quadrupled that, so $3.2 B revenue, and that they have greatly reduced their operating expenses (new servers, etc.) - so let's say they are making 50% net income, which would be almost impossible - that is still at best-case scenario $1.6 B a year, which hardly justifies $50B . Even the most optimistic growth targets are going to bump up against hard limits: people can't spend more than x hours a day online, there are maybe 5 billion users worldwide as a potential market. Unless the CIA is going to pay them a couple billion a year for data mining access (CIA's VC arm was an early investor) since we have all so nicely classified ourselves and our social graphs for "TIA" purposes, I can't see the valuation sticking.