Hiya I just came accross this http://www.spamitback.com/ and it looks like an interesting way to fight back spam. So far it's unfortunately only available as Windows Client. However one should be carefull on using this as it might conflict with your local law... But in the end, it's a intriguing idea.
If traffic wouln't nearly be free in some cases people would think of not using it cause of throwing money out of the window just for that... when doing anything back to spammers violence against them would give me more pleasure than just sending back any trash
If traffic cost money them spammers wouldn't care, after all they arn't useing their traffic are they?