I feel Jay's pain. With the old system we were spammed from time to time - sometimes severely. My approach was to ban some of the key words in their message, for example, the URL of the website you were supposed to visit to get whatever crap it was. That meant that the posts never actually showed up on the board - but they
did show up in our "messages awaiting approval" queue. At one point, someone was trying to spam us and repeatedly tried to post. There were something like 120 attempts in the queue that we had to delete. BUT only a few got through to the general public.
Registration helps a lot. We've only been spammed once that I'm aware of, and I was able to deactivate that user, as well as block his keywords. That doesn't mean it won't or can't happen again, it almost certainly will, but when it does, please feel free to report the message using the report message button.
Don