I'm on a few forums that have a "reputation" rating, and you can "like" or "dislike" a person, and it counts in their reputation...
not respected at all, not respected, neutral, respected, very respected... are the ratings.
So, I did a "dislike" on someone who in my opinion did something nasty... that person went to several of my existing posts and hit dislike on them, even though they were months old.
I've seen this in several places... if you give people the ability to dislike someone, it's often someone not really likeable, and they will often retaliate... and you are right down the drain.
I think the "neutral or like" system does work well... if you REALLY think someone is a doofus, then you have to tell them so ha ha!
Greg