How Privacy Vanishes Online

If a stranger came up to you on the street, would you give him your name, Social Security number and e-mail address?Probably not.Yet people often dole out all kinds of personal information on the Internet that allows such identifying data to be deduced. Services like Facebook, Twitter and Flickr are oceans of personal minutiae — birthday greetings sent and received, school and work gossip, photos of family vacations, and movies watched.
http://www.nytimes.com/2010/03/17/technology/17privacy.html