Facebook beat analyst estimates in the fourth quarter of 2012, with revenue increasing 40% year-over-year, thanks in large part to the success of the company's nascent mobile marketing campaign. The social network firm posted net income of $426 million in Q4, excluding certain items. Shares of Facebook's stock fell in after-hours trading after CEO Mark Zuckerberg said the company planned to spend more money to capitalize on new opportunities, which could limit profit growth in the future.