There's a nice step by step tutorial on Benzedrine.cx explaining how to get revenge on spammers by using tarpits. The author says:

"I don't like getting spam. The problem is not detecting it automatically, that works very well with tools like SpamAssassin and bmf. Even though I can automatically delete spam without reading it, the spammers still successfully deliver their mails and get paid by volume. I want to hurt them. They should not be able to deliver their mails, and waste as much of their resources as possible attempting to do so."

Skillfully employing tarpits (fake SMTP servers), the author in fact takes on the connection with a spammer who is trying to send spam, and answers really slowly, causing hang-ups and cues on the spammers server. This takes anywhere between 10 minutes and infinity, and makes the spammer much less effective.

If you're up to it, read the whole article and follow the in-depth instructions.