For a long time the only spambots ive had were casino and poker advertising, and they were easily defeated by a word filter.
However it seems the spambots are becoming more devious, passing on hidden form data, using bbcode links, and posting websites that seem innocent, but actually redirect you.
Well the guestbook has annoyed me too much, and I should not have to delete them, or force people become members. So I create a plugin to do a captcha image test for anonymous posts.
Its now running on this site, so let me know what you think !