I just read an article about messagelabs.com porn filtering s/w. It scans emails for porn by matching porn images against upto 22k different algorithims...serious stuff.
http://www.messagelabs.com/page.asp?id=567
I used to do a lot of mailing but stopped about 5 months ago.
Are most porn mails still getting through? better question is there still good money in it (it was very good before).