I know this is going to sound like yet more bickering (oh no) but I'd really strongly recommend either disabling the vBulletin reputation system or yanking the ability to give negative reputation. I've been active on forums that use this and it causes a lot of ill feelings and people stop posting out of fear of being neg-repped since it's so unmoderated and anonymous.
I'm all for giving people credit for their efforts, so how about just allowing positive rep points? This makes people happy and it becomes a positive thing rather than a method to rile each other up when you wonder who neg repped you.
And as a side-note, no I didn't get neg repped, I just saw the little green bars and became alarmed that they were being employed here on a site that is well moderated and pretty well under control.