Geez, talk about horror stories.
I watch what I post online, even though I really have nothing that needs hiding, and am very careful with my privacy settings. However after reading some of this I'm considering just deleting my Facebook before I head off if I get an appointment.
My advice, go into those security settings and lock down your photos. Do NOT permit friends to post photos without your expressed permission (they may not have their security settings set to friends only).
... It may be a photo of you, dancing naked on a table top, with one of those beer hats on.