I have Peter's Custom Anti-Spam on my blog (and on a friend's blog which I manage); I also have SexyComments installed, and I noticed that I have two CAPTCHA fields instead of one (with two different words).
It's not a bug report, just a FYI – I think it's actually good (isn't it? wouldn't spambots have a bigger problem figuring out two captcha entries instead of one?), and because I can customize the words, it doesn't bother the readers. One of them joked "Two CAPTCHA's? You got'em on sale?"
See an example here.