I joined an interesting project called Project Honeypot. It involves putting up scripts on websites that give harvesters addresses that are used to catch them spamming. You can donate mail domains to the project to make it so diverse that the address harvesters will have no way to know that they are harvesting Honeypot addresses. It seems like a very cool idea to catch these bastards before even a single email is sent. It will work because many harvesters also send from the same IPs, and additionally ISPs can be notified about harvesting and they can add TOS requirements that users not harvest addresses.