It's the end of May, and my evaluation period of Spam Karma 2 is complete. Spam Karma 2 is a Wordpress plugin that scores incoming comments based on a number of criteria. As an example, if a comment is being submitted less than 10 seconds after the "visitor" visited my site, it's probably a spam comment.
Here's some numbers for the month of May:
566 comments were submitted
491 comments were spam
29 comments had to be confirmed as spam
No comments from actual people were ever mistaken as spam
Those are some pretty good numbers. Because of the differences between how Akismet and SK2 work, it's not really possible to give an apples-to-apples comparison. I will say, however, that SK2 greatly simplified my life by hiding obvious spam comments by default; I only had to look at comments that were less obviously spam. During my test of Akismet in April, however, I had to verify every single comment. Yes, all 320 of them. SK2 has an approach that lets me skip comments that it's 1500% sure are spam and look at the ones it's only marginally convinced are spam. Further, SK2 never made a mistake per se. Akismet did.
I cannot imagine going back to Akismet. It's a great service, but SK2 proved to be more accurate, in addition to meeting my desire to use a decentralized spam fighting solution.