Business Model - Cost per Share in Facebook

Before the lecture on Wednesday last week, I always wonder why some websites, such as Youtube, facebook, Wikipedia, ect., let me use free. How can they make profit? Many questions about how online business can be profitable. But now, I have satisfied answers.

The link is an article about online business model: http://venturedig.com/tech/monetizing-social-networks-the-four-dominant-business-models-and-how-you-should-implement-them-in-2010/

One of the ways which facebook can make money is Cost per Share (CPS). It bases on number of people share the links on their news feed. CPS is higher than CPC because people who share the link, are most likely loyalty customers/visitors. This method is also a good way for business to spread the company's name. Because friends of the loyalty customers will believe the link is useful and harmless. However, the CPS can only work with well-known company's ads.