Bad behavior and Akismet combine to do the same thing (WP). The trouble is, you've made life more difficult for your users. On blogs, non-image "CAPTCHAs" are

Bad behavior and Akismet combine to do the same thing (WP). The trouble is, you've made life more difficult for your users. On blogs, non-image "CAPTCHAs" are trivial. (e.g., "Put 42 in this box -->"), so long as your site is low enough traffic that no one cares to write a bot targeting you.