In April, Facebook agreed to acquire Instagram, a mobile photo-sharing company, for $1 billion in cash and stock. But by the time the deal closed in August, the total price for the two-year-old startup was closer to $715 million as a result of Facebook's falling stock price following its initial public offering.
Facebook also made news this year when it reached 1 billion users. The challenge? Many of them are accessing the social network on their iPhones and Android devices, putting pressure on the company to figure out how to make more money from mobile. Growth in mobile advertising hasn't kept pace with the surge in members.