I've seen it on other forums I think whereby members earn a sort of Reputation Score based on their history and advice. Only issue I can think of is how to prevent it from being abused :P
That's the problem. I've seen this sort of system devolve into virtual open warfare with people "Revenge Repping" every post from someone who's upset them whilst upvoting their mates' posts.
Now, of course, I'm not saying that this would happen on these forums, since everyone here is such a kind-hearted, open-minded and forgiving soul and wouldn't let a difference of opinion or personal animosity drive such things, but I thought I'd mention it anyway...