http://www.nytimes.com/2012/02/05/opinion/sunday/facebook-is-using-you.html?src=me&ref=general

Facebook makes money by selling ad space to companies that want to reach us. Advertisers choose key words or details — like relationship status, location, activities, favorite books and employment — and then Facebook runs the ads for the targeted subset of its 845 million users …..

Ads that pop up on your screen might seem useful, or at worst, a nuisance. But they are much more than that. The bits and bytes about your life can easily be used against you. Whether you can obtain a job, credit or insurance can be based on your digital doppelgänger — and you may never know why you’ve been turned down. ….

full article:
http://www.nytimes.com/2012/02/05/opinion/sunday/facebook-is-using-you.html?src=me&ref=general

(by Lori Andrews, author of “I Know Who You Are and I Saw What You Did: Social Networks and the Death of Privacy.”)