I moderate a serious discussion forum on another board and we have some similar issues that ASC faces with new users. FYI: the board has something like 5,000 active users, 20,000 registered, and I'd say we have about 30 active (read as: good) posters in my forum. We also have many more random users coming in a posting stuff like "Is Dubbya more like Hitler or teh Devil???? LOLZ" or "Is cutting yourself normal?".
Serious Discussion (the forum name) exists for people to argue, debate and discuss issues in a serious, academically (or at least intellectually) rigorous way. In order to ensure this we have a very straight-forward set of rules which users are required to read before posting. Most of them do not do this and as a result we get lots of junk threads/replies being posted.
The way we deal with this is pretty hands-on, but it works well.
Whenever someone creates a junk thread, I simply lock it, toss it to the trash forum, and send the user a PM telling them why I locked it and how to go about posting it properly (pointing them to a FAQ, dictionary, spellchecker, etc).
Whenever someone replies with a junk post, I edit it out or delete it and then send the user a PM telling them why I did that.
Generally that brings two kinds of responses:
1) "Fuck you, man, this is a free Intarweb I can do wut I want...lolz"...I then give them the banhammer.
2) "Okay, thanks for the heads up."...I let them go on their merry way.
If ASC were to use a similar method, while it would cause the mods to spend more time moderating the boards, it would also ensure that we get rid of most of the stupid noobs, and keep the good ones.