Well... Actually it is free advertising, wheter it's good for publishers is another matter entirely...
"I wouldn't have bought it anyway, so the publisher did not lose any money." Is actually a pretty good argument, if the statement is true...
"File sharing is the inevitable consequence of technology, and copyright law should be ignored because it's outdated needs replacement." The first statement is certainly true, i also think that copyright law is way outdated, if you look at walt disney you would agree. I want to support good writers/publishers with my hard earned money, i just wish everyone on the planet (or even a significant amount) would feel the same way.
Pirates benefit from spreading these memes of rationalization around, because the more people they can persuade (at least up to a point -- if they persuade everyone, they kill the business), the more free stuff they'll get, as converts join the effort to scan books or share the commercial PDFs they've bought.
Yeah right! It's actually not good for pirates, because the more exposure, the more people will notice and the more 'enforcement' the scene gets. Only a small group of people actually scan/OCR books, the rest are just leechers. The leechers need the morale approval...
Did you know that this actually started as an effort to get out of print books and brake the ebay traders that asked $100s of dollars for sought after OOPs? The industry reacted way to slow, now they have a full blown pirate outbrake on their hands, serves them right!
I don't know that there is any effective way to stop piracy, but I do see some value in bursting the bubbles of self-delusion that pirates use to feel good about their wrongful behavior. Perhaps all we can do is try and maintain the guilt, and mitigate the damage it does to sales.
As many have already said in this thread, the results are anything but conclusive.
I could even speculate that you where always a very 'pronounced' anti pirate and started this project to proove the pirates are 'wrong', you might even have selected this specific product because it was clear in advance that sales would fall drastically the following year... I could speculate this, but i won't.
A different question though, how did the pdf products go that where for sale?