We still moderate the first three posts of every new user, however they have figured out how to post beyond that. We are working on a way to solve this.
I have a suggestion - indigo posted above that the post count is several per hour over a period of time. So, you could add a filter to the spam detector that if the same/similar IPs (or messages following a similar theme) post more than a certain number of messages per hour (e.g. 10/hour), their messages should be automatically "quarantined" in a queue before an admin/moderator releases them.
