Wall Street Journal: Even if you're very careful about which apps you use on Facebook, companies may be learning personal information about you through the apps your friends use. After examining the 100 most popular Facebook apps, the Wall Street Journal "found that some seek the email addresses, current location and sexual preference, among other details, not only of app users but also of their Facebook friends." It added, "Facebook requires apps to ask permission before accessing a user's personal details. However, a user's friends aren't notified if information about them is used by a friend's app."
The article notes that although Facebook is "free," users pay for the social networking service by allowing the company and its advertisers to have access to their personal information.