Now that Facebook is going public (reluctantly, due to a Federal Trade Commission rule) and is releasing financial statements we actually know how much money Facebook is making off of us:  about $1.21 a quarter according to Techcrunch.  This amounts to around $4.84 a year per user average.  This figure is of course only part of Facebook's income portfolio as it makes money off of advertising, investments, and licensing.  At times like these it is important to remember that Facebook is not ours, it is run for the profit of the shareholders.  The dozen or so iterations of Facebook that have been implemented over the last eight years have all had modifications that were put in place to maximize data mining and advertising sales. A worthwhile re-read at a time like this was done by a former blogger for this site.  Here are links to Amelia Northrup's social media analytic series:

http://www.technologyinthearts.org/2011/05/the-art-of-social-media-analytics-part-1/

http://www.technologyinthearts.org/2011/06/the-art-of-social-media-part-2/

http://www.technologyinthearts.org/2011/06/the-art-of-social-media-analytics-part-3/