One of my wife's friends got themselves into a sticky situation. When she first started using Facebook, she made the mistake of "Friending" her supervisor. Last month, she realized that she was uncomfortable with having her boss access to some of her personal information. Along with another co-worker who had the same problem, they ended up "unfriending" their boss.
As you might imagine, it did not end well. When the supervisor discovered the change, they both ended up having a tense conversation with her. While nobody got fired or disciplined, the incident harmed their relationship.
If you participate in social networking sites, you must understand that your actions can have consequences.