Facebook is ready to change its status from private to public - as in a publicly traded company. The leading social network officially filed paperwork for an initial public offering of up to $5 billion, which would make it the biggest IPO ever to come out of Silicon Valley. 　　The filing provides insight into the business of Facebook. Advertising accounted for 85 percent of the $3.71 billion in revenues the company saw last year, boosting profits to $1 billion. 　　Brian Hamilton is CEO of Sageworks, a financial analysis company. Brian Hamilton, CEO, Sageworks: "They are growing, they are profitable, the margins are good and they entirely own their space - and that's terrific. 　　But on the valuation side these guys are going to be priced at about 100 times profits and probably between 18-25 times sales. So it's going to probably be a richly priced stock if it comes out the way we think it will." 　　According to the filing there are 845 million active Facebook users, and a little more of half of them logged on, on average, each day in the month of December. 　　That's keeping CEO Mark Zuckerberg busy and rich. His total compensation for 2011 was just under $1-1/2 million. His base salary will drop to $1 next year. 　　Morgan Stanley, JP Morgan, and Goldman Sachs, along with a few other Wall Street firms, will help bring the offering to investors. There's no word yet on which exchange the shares will be listed. (Conway Gittens, Reuters)