It's been clear for some time that Facebook is big, but industry watchers are about to get an idea of just how big. The social network today announced its initial public offering, and The Wall Street Journal reports the IPO could see the company valued at as much as $100 billion.

　　Most expensive book ever. That would make the company the biggest tech IPO of all time, easily topping the 2004 Google IPO, which saw the search giant valued at $23 billion, raising an extra $1.9 billion in the process. The Facebook IPO is expected to raise between $5 billion and $10 billion for the social network.

　　Facebook's long-awaited publicly traded debut follows that of another online specialist, as social game publisher Zynga had its own IPO late last year. That company--which relies heavily on its Facebook games--disappointed industry watchers, debuting at $10 per share and finishing its first day beneath that level. However, Zynga shares have since recovered, finishing today's trading at $10.60.

　　In its filing with the SEC, Facebook acknowledged the important role that social games play in its business model, saying that they "are currently the most successful apps" on the network. The company also indicated that it derived $557 million in revenue from the sale of virtual goods in 2011. These revenues are derived from its Facebook Payments monetary system, which all game developers must use when selling in-game virtual goods.

　　For 2011, Facebook reported $1 billion in profit off $3.71 billion in revenues. The exact date of its IPO, the number of shares, and the price at which they will be set have yet to be determined.