I have an idea that may help. What would you think about making it so a new member has to use a captcha for their first 10 posts or so. Maybe even for all of their posts until it has been verified somehow that they are a real person and not some bot. Yes it would be somewhat annoying to new members but if it helps to reduce spam then I think everyone would be ok with it. This is my first post and I would rather have to go through some 'initiation' like that then see a great looking page be overrun with spam. :)