I know it's a bit late and all....but the stackoverflow model works for a few simple reasons:
1. other people vote up/down your answer, and not you personally
2. it is only based upon how others view your responses that you can collect all the 'badges' and stuff
3. people who are very active will get a range of badges and stuff and can even become moderators through good,positive use of the system.
So, for people who like badges and karma and stuff, go for it. Others can ignore it, no problems.
However by ranking the answers based on up/down vote, the dynamics of the system change from a 'Thread/Topic' scenario to a 'Question/Multiple Answers' scenario, which is exactly what goes on here at arduino.
...but like I said: it's a bit late to suggest it
In a standard forum like this, i'd drop it.
 I thought I'd add a link to an open source stackoverflow style system (even though it's too late):http://www.osqa.net/