I moderate on several forums, and I think the best advice I've seen given is to "give the user the benefit of the doubt". Many new users may not have much experience in forums, and so are unaware of the typical 'netiquette'. Or they may come from another country/culture, and English is a second language for them, so they failed to fully understand a rule. I think it's important to look at one's post and analyze it in context, and then, if it looks like an infraction, handle it with the least necessary force. A PM may suffice... perhaps an infraction is called for... occasionally it's patently obvious that they were fully aware they were breaking a rule, but decided to do so anyway, so you give 'em the boot! I've found that consistency is the best teacher. If all the mods are singing from the same book, and each responds fairly and similarly to issues, whether they are in agreement with the poster or not, they build credibility as a group.
Whenever a large group is brought together, there are bound to be disagreements. Moderators ideally (IMO) try to steer things in the right direction when possible, but jam on the brakes only when really necessary.
Members, on the other hand, need to remember that mods are often constrained, either by the rules set forth by admin, or by their inability to express their own opinion fully, lest it reflect poorly on the board.
BTW, I agree wholeheartedly with the comment about the difference between being a mod and a member, when posting. Not always easy to do, I realize, but mods deserve the opportunity to post on the forums as members... let their hair down a bit... without being seen as the bad guys. Their voluntary actions help make the board a lot more pleasant for the rest of us.
Just my two cents worth.