There's nothing wrong about making your product more fun by introducing gaming elements. Yahoo includes them in their design patterns http://developer.yahoo.com/ypatterns/social/people/reputatio...

Twitter has no "game" elements? Why do they display the number of your followers to everyone then? Doesn't Facebook show the "likes" of your stories to everyone? Or the number of your friends? What about everyday life, don't we go to school and get grades and distinctions? I even think its a fun concept philosophically, after all, life itself is a game.