Image via WikipediaFacebook has so far never made an acquisition. Acquihires like Dropio and Hot Potato don't count. And a company can not do internal innovation forever. The price you pay to get big is you are open to innovation from outside. You keep a clear vision of where you want to go as a company, and you make acquisitions along the way in emerging spaces and sub spaces.
Facebook was ready to go IPO last year based on its fundamentals. But a recession perhaps was not a great time to go public. But now the recession is over. Further delays will cause Facebook harm. To put it down bluntly, Facebook can not make GroupOn like acquisitions if it stays private.
You can't do big things if you don't have big money. Both Facebook and Google compete in the local space, and Google just scored a big win. It was about having money, it was about having cash in the bank.
For Facebook going IPO is like asking out a girl you really like. Facebook is acting hesitant although it is quite a good looking lad. That diffidence will have to go at some point. Capitalism asks for that diffidence to go.