“If you used to have to send fifty thousand pieces of spam to get a response, now you have to send a million,’’ John Scarrow, the general manager of anti-spam technologies at Microsoft, told me. (Spammers usually need to send a million e-mails to get fifteen positive responses; for the average direct-mail campaign, the response rate is three thousand per million.) “Spammers just shrug it off and send a million.”
A great overview of spam, with tons of interesting tidbits like the above.
Unfortunately not an article that offers much hope.