Who can see what you post on Facebook is a tricky concept. After numerous complaints FB made a lot of changes to their privacy settings but it’s still complex, and not all of the settings are “sticky” – you may think you are fine but unknowingly did something that makes everything you subsequently post a LOT more visible than you thought.
The most dangerous privacy slippage I’ve seen recently is one that may be setting ALL your status updates to be publicly visible – including to job interviewers, co-workers, etc.