Stopping Comment Spam with hashes and honeypots (and not CAPTCHAs)
Very nice write up of some effective (for now) techniques to stop the two main types of spam bots.
Hashes prevent replay attacks, and honeypots pevent form-filling bots.
Fun aside: Ned is the guy with instructions on how to make a cube out of six business cards. I did this a couple years ago and it was pretty cool.