Facebook says in its IPO filing that it has 845 millon users worldwide. This is up 39% from the prior year. Revenue is up 88% from the prior year. Facebook's 2011 revenue is $4.27 billion, according to eMarketer. Facebook's 2011 profit was up 65% from the prior year. Analysts say costs and expenses are growing faster than revenues. R&D costs including employee hiring and equity compensation went up to $114 million in 2011 from $9 million in 2010. Facebook had 3,200 employees in Dec. 2011, compared to 2,172 in the prior year. Revenues come from online ads. Ads on the Facebook site increased by 42% in 2011 over the prior year, and average price per ad increased by 18% in this period. Ads are generated using the information provided by users on demographic factors, age, location, gender, education, work history and specific interests- so that subsets of users can be targeted by advertiserrs of products.