Now, how do I get it to actually work?
Whether or not I click on the I am not a robot check box the form gets validated and sent.
UPDATE:
Turns out I was assuming it would be more difficult than it was. In case anyone else has problems, here's what you need to do:
1. Go to http://www.google.com/recaptcha/admin to get a new key pair
2. In CMSMS, go to the Captcha module and set the Active Library to reCaptcha.
3. Set the Key pair values on the reCaptcha Options page
4. Turn on Captcha for the form(s) that you want.
One thing that I also did was to delete the Help text for Captcha in each form.



