James Seng’s blog: Bayesian filter for MT. What it says. An alternative to MT-Blacklist. By the same guy that wrote the captcha doohickey.
I’ll take a peek at this but Seng’s got a hard row to hoe with respect to ease-of-installation; MT-Blacklist was a model of an MT plugin, whereas the captcha code was relatively hackish.
In the comments on his entry Seng notes that he believes the filter should be interoperable with MT-Blacklist.