Stopping Comment Spam with hashes and honeypots (and not CAPTCHAs)
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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.