Akismet now has API documentation and not one but two Python implementations. The WordPress plugin has also been updated to respond to the most common feedback and a few minor bugfixes. Akismet has caught 465,769 spams since it started (81% of all comments) and is protecting over 35k unique blogs.
It’s an amazing piece of work.
Speaking as the author of one of those Python implementations, part of its amazingness is that it does manage to have a very clean API. It was literally the work of about 45 minutes to write the code to handle talking to it. (And then another two hours to realise that I’d made a type in “user_ip”, and write the documentation and examples.)
Much easier than some of the other APIs I’ve had to work with.
Given your more recent statements about working well with SK2 and BadBehavior, perhaps you should update the Akismet FAQ answer for “Should I use any other spam plugins?”
Anyway, this is really good stuff!