The rule is "No karma camping" In the past this has consisted of someone getting annoyed at someone, finding every one of their posts, and rateing them into oblivion.
Generally:
If it is an estableshed poster, and a 15 post ratebot rates them down, the bad rateings will be removed
If it is an abnoxious newb spamming crap on purpose and they are karma camped for being annoying, They are fair game. Hell, I'll help
If two estableshed posters go after each other, generally nothing is done untill it becomes too big of an issue, or spills over to other people.
If someone is being an annoying little twit, nuke em. Just make sure you pick your targets well. Out in the other forums, things are a bit more regulated, but in here, as long as it doesn't get out of hand. Generally a public "stop karma camping people <insertnamehere>" works, if not, they get norate flag.
There are some people that rate in here, mostly good things, or nuking trolls. most people don't