User blog comment:IamJakuhoRaikoben/Fairy Tail Wiki Family Tree/@comment-4699821-20120310160817/@comment-3987368-20120310171045

To break it down simply: they track all your account's searches, every link clicked, every rating applied to every one of their sites (like YouTube, Google search engine) and STORE IT ALL. It can, with your permission, be shared to 3rd parties (other companies) and adverts will be personalized based on all of this. Worst of all: no way to opt out.