I haven't been banned, nor warned.
I moderate a few boards and am usually easy-going about SOME things, but I always note what I don't think fits the mood of said forums, then I send a private message, then I suspend, then I ban. I think I have a good theory of how to moderate.
Basically, as long as people remember that the other person on the computer also has feelings, they are being good diplomats and promoting a positive feeling, staying on topic, not calling people out or continuing arguments, and are not spamming then it's all good.