You can see the dropoff in my corporate spam reception at http://jim.studt.net/spamdrop.png . At about 3pm central standard time about 40% of my spam stopped arriving (red line and zinc chromate green line). Not bad for a single action.
(The vertical axis is "messages per hour". My filters are lined up as bogofilter,dcc,spamassassin,clamav. A positive for spam stops evaluation of the later, more expensive filters. Likewise, most viruses are caught in the spam filters and never get to clamav. The robots line is automated status reports from remotely deployed code.)
Unfortunately, actions like these do not knock off spam for long. iirc, the last time a major spammer was knocked offline, the result was a sharp drop for a day, then a return to pre-action levels.
We're better off making spam a less profitable venture, and thereby letting the market reduce the number of people turning to spam as a source of income.
(The vertical axis is "messages per hour". My filters are lined up as bogofilter,dcc,spamassassin,clamav. A positive for spam stops evaluation of the later, more expensive filters. Likewise, most viruses are caught in the spam filters and never get to clamav. The robots line is automated status reports from remotely deployed code.)