UPDATE: I would highly recommend Gravity Forms from RocketGenius for a very robust form integration with WordPress!
I've left comments on Ryan's site and IM and told him that I was able to fix the issue by adding a Challenge Question, but I can't seem to get in contact with him. So… here's Ryan's plugin with the new and improved Spam Protection. I am using it on my site and it's working great.
The Plugin can now be downloaded via the Project Page: WordPress Contact Form with Spam Protection Plugin Project Page