Each of these pieces of information (and misinformation) about me is sold for about two-fifths of a cent to advertisers, which then deliver me an Internet ad, send me a catalog or mail me a credit-card offer.
Data Mining: How Companies Now Know Everything About You
Time, By Joel Stein, Mar. 10, 2011
In the past few months, I have been told many more-interesting facts about myself than my Social Security number. I've gathered a bit of the vast amount of data that's being collected both online and off by companies in stealth - taken from the websites I look at, the stuff I buy, my Facebook photos, my warranty cards, my customer-reward cards, the songs I listen to online ...
Google's Ads Preferences believes I'm a guy interested in politics, Asian food, perfume, celebrity gossip, animated movies and crime but who doesn't care about "books & literature" or "people & society." (So not true.) Yahoo! has me down as a 36-to-45-year-old male who uses a Mac computer and likes hockey, rap, rock, parenting, recipes, clothes and beauty products; it also thinks I live in New York, even though I moved to Los Angeles more than six years ago. Alliance Data, an enormous data-marketing firm in Texas, knows that I'm a 39-year-old college-educated Jewish male who takes in at least $125,000 a year, makes most of his purchases online and spends an average of only $25 per item.
... Each of these pieces of information (and misinformation) about me is sold for about two-fifths of a cent to advertisers, which then deliver me an Internet ad, send me a catalog or mail me a credit-card offer. This data is collected in lots of ways, such as tracking devices (like cookies) on websites that allow a company to identify you as you travel around the Web and apps you download on your cell that look at your contact list and location.
and Joel Stein conclusion:
Oddly, the more I learned about data mining, the less concerned I was. Sure, I was surprised that all these companies are actually keeping permanent files on me. But I don't think they will do anything with them that does me any harm
CNN interview with Joel Klein about his Time cover story
The article also mentions other companies which provide personal information: