In my previous blog entry on some plan(s) for spam, I mentioned that I didn't care for challenge/response "human-only" whitelists. I couldn't put my finger on exactly why I felt that way.. until I happened upon this John Graham-Cumming PowerPoint presentation:
This is a companion discussion topic for the original blog entry at: http://www.codinghorror.com/blog/2004/09/popfile-vs-popfile.html