This was just too easy. The module makes implementing captcha trivial, plus you'll also get karma points for helping digitize books. The most difficult part was reading the terms of service when registering for a reCaptcha account.
Works out of the box, minimal dependencies, beautifully documented, with an easy to use API. I went from nothing to having fully working reCAPTCHA support on my site in less than 30 minutes, which included registering on the reCAPTCHA site and using dh-make-perl to build the module into a .deb fiile.