I made a "karma" hack way back in the day... and have been slowly working on one for 7.x. My time is extremely limited nowadays compared to what it used to be, so if you guys want to make it an official feature, I wouldn't complain!
What I'm trying to do with this one is have it so there is a +/- link (of sorts) with each post. One link to say it's a good post, another to say it's garbage. This will build up, or knock down, people's "karma points." The number of points a member's karma click of a post would give or take away would be set by group. Also, a group may only give a karma click to any given post once (first come, first serve) with the exception of administrators and moderators. This could be permissions-based too for any group. Finally, the reason I want to do this at all, this would be tied in to automatic promotions. Once reaching a predetermined number of points, a member will be promoted to the next group, and vice-verse if their points drop. I have never been one to award titles or ranking completely based on post count -- I'm more of a "quality" person, and this is the perfect solution.
Anyway, I know it reads like a lot, but it's a simple mod that can be finished in less than a full day's of work I'm sure.
