[xoxoxoBruce]

boingboing says

If you get a spam email, simply forward it to sp@mnesty.com, and Spamnesty will strip your email address, pretend it's a real person and reply to the email. Just remember to strip out any personal information from the body of the email, as it will be used so the reply looks more legitimate. That way, the spammer will start talking to a bot, and hopefully waste some time there instead of spending it on a real victim. Meanwhile, Spamnesty will send you an email with a link to the conversation, so you can watch it unfold live!

Here's one where they tied up a spammer for 9 months.