For disruptive mobile payments startup Square, 2011 was a year of massive growth on many levels. The startup ended the year with over 1 million merchants using the mobile payments platform to accept credit cards (there are only 8 million merchants who accept credit cards in the US). In November, Square announced it was processing $11 million in payments per day (up from $4 million a day in July). Sir Richard Branson, Kleiner Perkins, Visa, and other investors poured over $100 million over the course of the year into Square, with the company’s latest valuation pegged at $1 billion. And Square announced a number of new product innovations, including Card Case, a new iPad app and more. Not to mention the unveiling of retail deals with Apple, Wal-mart, Best Buy, Radio Shack, and Target. It’s hard to imagine how Square could top such an eventful year. But according to COO Keith Rabois, 2012 will prove to be even more monumental for the mobile payments company.