Constantly changes privacy terms without adequately notifying members. Third party add-ons/games/quizzes are not appropriately screened for privacy policies. Site has been hit multiple times with phishing attacks and responded too slowly to correct the situation.
The connection is not secured through SSL and until otherwise proven, any application written - whether it's a game or quiz application can access all your personal and contact information, including internal messages unless explicitly denied.
Not a site for children!!! How many children will know how to configure the settings properly. The site is a social networking site and spreads your information all over the place. Including outside of Facebook if your not careful. Parents think twice about letting your child on here or any other similar site.
Although Facebook can be generally safe if used appropriately, there is a high risk of running into privacy issues. As you would probably know, information acquired on the site can be used for a variety of illegal means.