Looks like a winner to me! Captcha has been a very frustrating, but necessary, evil. Looks simple enough to integrate. Might be a nice plugin addition for a future release:
I have it on my site and seems to be working well, just register on the captcha site enter a couple of details including your domain, get your captcha keys(twoo sets) and off you go.
No problems so far with the reCaptcha, you have to register at the reCaptcha site here: http://www.google.com/recaptcha then it will give you two sets of keys to enter in the admin section of your nop site, and thats all.