It will be great if there is a point system into it. For example if somebody write down a guestbook he get points. Or when he played a game(joomlaflashgames) and get the highscore he get 10 points and he 2nd place he get 8 point and go on.
And when he invite some friends he get 2 points for each invite.
and when he gives comment on a article.
This will be great if this will happen.