I've been using WP Hashcash in conjunction with Akismet and so far every comment that has come in has been put into the spam queue, including comments that I have made myself. They all say:
[WORDPRESS HASHCASH] The poster sent us ‘0 which is not a hashcash value.
Also, how do you identify a false positive? I see that I can remove the above message from the post and then approve it. Does this plugin let you identify false positives or is it only Akismet that does that?