For what I know, if people like your posts they applaud and you gain +1 karma, if they don't they smite and you get -1. I've already seen that on a few other forums. Some even calculate a "positive ratio" = applause/total votes = applause/(applause + smite), giving something between 0 and 100%.
You'd be right in what you write. People can give you a +1 for a good comment, or -1 if they don't like your comment or generally hate your guts.
There's different types of "praise" on different types of forums. Unless you're super sensitive to what it means and your popularity, I wouldn't let it bother you too much. Although some people would be giving a subtle hint to write better posts / stop behaving like an obnoxious child.
