Like any other advertising-supported company, the thing that Facebook sells is eyeballs. Now baked into every post for Pages — and in testing for users — is the ability to pay to make sure more people's eyes cross your content.
I'm not sure if the average user is naive enough to believe in the benevolence of the News Feed and its algorithms determining what they see every time they login, but I'm curious to see how they ultimately react to learning more and more spots in their feed are bought and paid for. (via)