Facebook has plenty of revenue streams. Paid ads mostly, but they've also acquired a number of other companies like InstaGram, for example.
They are also in the beta stages of rolling out a "featured" post option where a user would pay to have their post appear at the top of a users "wall" instead of getting buried quickly as time passes.
There is also talk of on-site ecommerce of some sort to sell products.
While this may hurt user experience ,it will create more income, which will increase the value of the company.
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