As I am one of the developers of tag2find, I am also writing in the tag2find developer blog from time to time. This blog is a WordPress blog. One of our main problems there is fighting SPAM. We get literally dozens of SPAM comments a day. To limit the amount of SPAM visible on the blog itself, I found a very simple solution, which up to now did not produce any false positive: if a posting contains more than zero links, it will be held in the moderation queue.
WordPress offers this possibility out of the box, but the default is set to more than 2 links. I tried to limit it down to one, but this still missed to many SPAM attempts. Therefore I now have set it to zero. This works remarkably well. No SPAM postings anymore and we had just one or two false positives, which are not so bad as the comments are not deleted but just held for moderation.
I know, this is a very low-tech approach and puts some work on the maintainer of the blog, but it works almost out of the nature of SPAM, which most of the time wants to deliver links to pages to influence Google PageRank and/or lure people onto the website.