Currently, I put a validation step in the coupon savings new user registration that forces a user to wait until I can verify their email before giving them an account. This is annoying, as a captcha should work okay (I hope).
Dead Programmer's Society had an article on implementing captcha in rails backed by Recaptcha. Recaptcha is cool, as it uses words from digitized books that couldn't be understood by an OCR. So, as people use Recaptcha on my site, they will be helping digitize books. Look at it; it is pretty cool.
Let's see how long it takes me to get it integrated.
[Update: Well, it appears that following the instructions in the blog post worked, and I have captcha up in the new user registration. I haven't uploaded it to Heroku, yet, as I want to test a bit more on my local and make sure it really does work.]