" What was once an anonymous medium where anyone could be anyone—where, in the words of the famous New Yorker cartoon, nobody knows you’re a dog—is now a tool for soliciting and analyzing our personal data. According to one Wall Street Journal study, the top 50 Internet sites each install an average of 64 data-laden cookies and personal tracking beacons when you visit them. Search for a word like “depression” on Dictionary.com, and the site installs up to 223 tracking cookies and beacons on your computer so that other Web sites can target you with antidepressants. Share an article about cooking on ABC News, and you may be chased around the Web by ads for Teflon-coated pots. The new Internet doesn’t just know you’re a dog; it knows your breed and wants to sell you a bowl of premium kibble. "

Revisiting this and also this.