I did a lot of tests with it (in my dev environment only), and I've also noticed that a lot of spammy *content* was not intercepted.
So I also had some doubts about it ![smiley smiley](http://www.question2answer.org/qa/qa-plugin/wysiwyg-editor/plugins/smiley/images/regular_smile.gif)
After a research on internet I found that their algorithm is "secret", but it looks like that it does not consider only the "content" of a post, but also other factors such as the IP address from where the post comes. For instance, if your IP is not on its black-list AND it's the IP that is invoking the Akismet's API, the algorithm could conclude that the poster is trustworthy (so the return value is False).
However I think it has other main issues too (that I've already submitted to the author
)
I think however I'll give it a try