If this were standard marketing behaviour, I don't believe it would be nearly as effective.
For all the works that have their sales increased by the extra exposure that piracy can sometimes give, how many do you think have their sales reduced by piracy due to, y'know, piracy?
This is my major problem with the riaa/mpaa/etc. They're trying to criminalize normal human behaviour (not paying for something), in the hopes that that will alleviate their piracy woes. Now, there are two parts to that last sentence. We may argue over the moral value of piracy, but that's not the point. The idea that, by criminalizing sharing, they will somehow prevent it, is ludicrous. If they had taken the tens of millions of dollars they've spent on lawyers and instead put it towards market research, if they had hired people to build them a workable economic model, then we wouldn't be having this conversation.
I can moan and complain all I want about the fact that people are copying my work without giving me money, but at the end of the day I'd be much more productive were I to spend that time and energy finding a way to entice them to pay for it.
The reason this hasn't happened is simple: The big money in recording is the production houses, and they're fast becoming irrelevant. They know as well as any of us do that a digital age economic model that sees content creators fairly compensated for their works will necessarily cut them out of the loop. So, instead of addressing the problem, they lobby and sue and try to cling to some semblance of relevance. Look at what Valve has done with Steam: It's no longer necessary for a game company to sign with the likes of EA or Activision in order to sell their games. The next step, of course, is to find a way to market independent titles effectively. The system isn't perfect, but it's improving, and it provides a model for content creators in other forms of media to emulate.
If it's the author's engagement that caused the spike in sales, what happens months down the road when the author's post is forgotten, but the pirated bits are still floating around in torrents?
While the effect looks positive today, it's entirely possible that the long-term result is negative.
However, the spike in sales would never have happened if the book hadn't been freely available to start with.
This is a measurable demonstration of a working business model, and it is, clearly, not the model the publishing business is using. Indeed, it is precisely this model that they are lobbying, and succeeding, to make a criminal offence.
It's absolute madness.