Basically, people give you positive AntiPoints if they think that your post was really helpful/good/enjoyable/etc...
People give out negative AntiPoints if they think your post was totally irrelevent/bad/disgraceful/rude/etc...

As you can see under my name, I don't give out much AntiPoints. I've only given out a few positive ones, no negative ones yet. I only give them out if I think someone is really great informative post - I don't like the idea of just dishing them out for every post I read.

Greg