I run this and the Cheater’s Guide blog open, which means anyone can swing by and say whatever, but they’re moderated, the other more heavily than this one, and I’ve got the built-in spam comment thing on. They catch ridiculous amounts of spam. I can’t even believe how much. And I haven’t seen a false positive on either blog yet, and I’m reasonably diligent about scanning for them.
So, here’s the weird thing. At USSM we use registration, which means you have to provide an email address and get signed up, ensuring at least that there’s some fairly low bar for users to leave comments. Since we went to registration, I’ve seen only a few dozen spam comments, almost all of those caught by content filters for keywords (or secondary criteria I set up).
I cranked Akismet up a while ago there, and its false positive rate in that environment is 100%. Every comment it has identified as spam was an actual message. None of them particularly worth keeping, sure, but all of them were real comments.
It’s interesting to me that given a target-rich environment in which spammers dominate, Akismet absolutely shines, but in a target-poor environment with no spam, it seems like it gets bored and starts picking off passer-by.