Stopping "form spam"

The other day, one of our customers asked for some ideas about stopping web-bots from spamming on her FrontPage forms. Many of you have probably noticed this form of spamming has really become commonplace the last few years. I found a good writeup by the techs at CommerceStreet with some easy to implement ideas to stop the spamming of your FP forms. The security code idea is brilliant...

http://www.cibd.com/Support/BlockingFormSpam.htm

Has anybody else in the group taken any measures to combat form spam on their site? If so, let us know how it's worked out for you.