I use Web Watcher. It has a keystroke monitor. You can read e-mails and IM's through Facebook anyway. I think my daughter uses GMail and for some reason, I can't see those e-mails. I have signed in as her before,though, to look. You can set Web Watcher up to flag suspicious activity about meetings or key words.
I haven't seen anything to be alarmed about with my daughter. She knows I can monitor what she is doing, but I don't think she realizes how much. If I saw anything suspicious, I would clamp down on her privileges pretty hard. I think it is impossible to fully monitor them because you would have to spend as much time as they do on the computer to see what they are doing.
