This one Facebook post and following conversation holds much wisdom:

• Don't forget to log out of Facebook when using a computer that belongs to someone else or letting someone else use your computer.
• Don't engage in behavior that someone would find objectionable if that someone is paying your tuition.
• And most of all, never, ever assume you have much privacy on Facebook.

People are CONSTANTLY getting embarrassed, fired, divorced, etc. from the things that are discovered on Facebook because they can't figure out how to keep it private. Your privacy settings are there to help, but often aren't enough (usually because they're not used properly).

Even if they were, hackers find ways in and marketers are buying your information directly from Facebook anyway.