You could also put in a rating system where people can give "kudos" to the people that post intelligently and take away kudos from idiots. That rating would show up under their name in every post so both they and others can see it... I would help to eliminate some of the junk posts and the obvious trolling. You could even set it up such that a user could self ban by reaching a certain level of negative feedback. It would hopefully keep people from being blatant trolls...
Also, give the mods the ability to delete or at least "hide" a response. When you get something that is blatant and the user gets banned, it becomes a stain in the thread that needs to go away promptly. You could just have the mods mark them as "hidden" and let you do the actual delete so that someone doesn't go rogue on you, Ioi...