It’s one of Facebook’s dirty little secrets, even though it’s been publicly available information for more than a year. Facebook takes information that you post, and sells it to advertisers who can use it in ads that are displayed to your friends. For example, if I posted “Eating Ben & Jerry’s Cherry Garcia ice cream”, Ben & Jerry’s could then show an ad to all of my Facebook friends saying “Anne is eating Ben & Jerry’s Cherry Garcia ice cream – shouldn’t you too?” The service is part of Facebook’s “Facebook beacons” service for advertisers, and the ads in which your Facebook info is displayed are called “Facebook Social Ads”. And if you don’t explicitly opt out of them, then you are fair game.