There is already a system in place that stops the vast majority of spam that I'm continually poking at so that new messages that get through are picked up in future. On a daily basis we handle between 100 and 500 messages in the moderation queue, this is with CAPTCHA, email confirmations and screening against a known spammer IP DB. The nature of the beast is such that the messages continuously change and evolve in order to get past the filters, what you see getting through on the boards is what happens when they manage to do it. There is a fine line between stopping all spam and making the forums uninviting and unfit for purpose, new users do need to be able to post without being moderated, because once you are in the spam queue its very easy for a legitimate message to get treated as spam. Not to mention a lot of new users post asking for tech support, having to go through a moderation queue before you can even think about getting help is not practical.