Since its initial public offering in 2012, Facebook has changed the world and made impressive progress on its goal of connecting the world. Today, the company counts roughly 2.2 billion monthly active users across its platforms. The social network has also delivered impressive returns for shareholders, with the stock up more than 400% since market close on the day of the company's IPO.Facebook still has big opportunities ahead, but its massive size suggests it will have a more difficult time delivering relative growth going forward.