I actually went to a speech a year or two ago that talked about our privacy on the internet. What the video said is true. Facebook and other sites online actually sells our information to companies like google so that they can directly market to your taste. I'm not too sure what else they do with the information but they do have an account created on each person that creates a sort of profile/personality so that they can know more about you then what you expect. Sort of scary I guess. Information in the wrong hands can really lead to some scary stuff I think.
http://www.readwriteweb.com/archives/facebook_sells_your_data.php
That article does the issue a little justice but I can't find anything about the personality databases