Yes, such feature would be nice to have. As I saw on, say, IP.Board forums there are "Like" buttons for every post, so one can gain reputation on forum by the amount of Likes of his posts.
Hi, we used to have a rating system a long time ago at http://old.nabble.com/ . Some people eventually got sad when their posts had gotten a few "likes".
It was't causing a satisfatory reaction, so that we removed this feature.
Do you still want it?
Well it is a good idea but as you say some of my members also thought it might lead to people being upset at their posts not getting 'liked' so I think I'll not bother for now thanks.