The problem is that just about any system you can create can be gamed, and good luck trying to figure out how it can be gamed before hand. Of course, the other problem is that us "Type A" personalities attach far too much weight to something that is essentially meaningless, so you get people exerting vast amounts of time and effort to maximizing their rep or minimizing somebody else's.
(And because I'm a big hypocrite but am trying not to be, I'll make this CW)
