Reading through the FTC Spam Summit Report (472k PDF), I came across an interesting study they did, buried way back in the Appendix.
To determine how effective ISP spam filters are, they created 150 fresh new email addresses, and posted them at 50 locations around the Internet:
“The 50 Internet locations included websites controlled by the FTC and several popular message boards, blogs, chat rooms, social networking sites, video posting sites, and sites with user-generated content that had high hit/visit rates.”
Then they measured how much spam they got, how fast, and how much their ISPs’ spam filters blocked…