Face Book and Sick Days

I was talking to a young woman the other day who had gotten into trouble with her manager who read a posting she had put on Face Book on a day she was supposed to be home sick. She was genuinely ill with one of those loose wet colds that make you back away whenever the person is near. Bored with TV, she went onto Face Book. The manager (who read the innocuous comment after her shift was over) sent a snippy note to the effect that she was glad the young person was all better.

Recently, someone else lost their job for using Face Book on a sick day. Her posting, however, was a negative comment about her boss.

Is this the sign of the future? If you are away from work, should you be banned from using Face Book? Or only for saying certain things on it? What about your emails? Should you be forbidden from replying to emails when you are sick?