About 2.5 years ago, when I changed ISPs, my SPAM rate went down from a few per day to 2 or less per month.

A while back my ISP started a complimentary 3-month trial of the Postini service for all of its users, advising that it would optionally be available by subscription after the 3 month trial.
During that time my SPAM rate was no different than normal and I saw NO EVIDENCE of any change in the handling of my e-mail. As the 3-month period was about to expire the ISP advised that due to a technical error most users had NOT been enrolled in the trial. They were going to re-do the 3-month trial starting immediately.

A few days after the trial (really) started I got a Postini 'notice' that I had junk mail that could be reviewed.
I went to the link and found over a dozen messages, some of which were things that I subscribe to that it had categorized as SPAM. I "told" Postini" to allow those (subscribed) mails through and to delete the rest. Approximately every 8-12 days thereafter for the trial period I got a similar notice, with fewer of my subscribed things as time went on (I don't subscribe widely, just to 4 or 5 things). I also had one virus warning and it turned out that my son's machine had been infected with some virus and had sent itself along to me. IMPORTANTLY... during the whole trial not a single SPAM came directly to me.

When the trial ended, and primarily because of the virus experience, I decided to subscribe to the Postini sevice for the fee of $1.00 per month.
SINCE doing so I now get SPAM directly to me, seeming to be able to bypass the Postini checking. In addition, the rate of SPAM notices continues at around every 8-12 days.

I AM HIGHLY SUSPICIOUS OF THIS "SERVICE"!
Based on my prior (before there was any "trial" of the "service") rate of SPAM messages it sure looks to me that this thing either generates SPAM or forwards existing SPAM to me as well as to original addressees!!!
HOW WOULD I KNOW. . . there is no way that I know of for me to know, but I do know that it would be in the "service"'s "interest" to do so, to make it appear valuable as a SPAM filter.

If you have any comments on this, I'd like to hear them.
Thanks