I have not looked at Akismet. Interesting idea, that! Thanks for bringing it up, Diego.
Another idea. Why not offer me a public key certificate that would let me authenticate each post I make on the forums automatically through the login process? The login could be certificate based. Anyone who has a certificate-based login is exempted from using Captchas when posting. How would I get the certificate? I could apply for one, pay for it, and get an email containing an activation link 24 hours or so later. I don’t mind paying a $5.00 fee to help defray costs. Or I could get one free, provided to me in the same manner, on any order of both a print book and an ebook with Pragmatic Programmer.
I think a transaction involving a payment plus a waiting period to obtain the public key certificate would eliminate most or all spam robots.
Bob