Not necessarily the same as books, but may be somewhat relevant.
There was a Japanese think tank that recently released a report that found the online piracy actually boosted the sale of anime DVDs.
http://torrentfreak.com/internet-piracy-boosts-anime-sales-s...
Personally, I used to work in the music business for Nettwerk Records (hence the Nettdata username), Sarah McLachlan's label. We were one of the few labels that believed that the freely available online versions of songs actually stimulated sales, especially for back catalogues.
When Sarah's Surfacing album released, we actually ripped high quality MP3 versions of the songs and hosted them for free download. We also created a streaming "radio" site that allowed you to make and play your own playlists from any and all of the songs Nettwerk had the rights to.
We had real live numbers that showed sales were up a LOT after we made things available online.
I think more than anything the content producers are being forced to rethink their models, especially when it comes to the record industry.
If they made their back catalogues available in an individual song format for a reasonable price (whatever that would be), I think they'd do well.
And for what it's worth, I actually bought a non-DRM'd eBook this morning, one that I can read on my laptop in PDF, or on my iPhone and iPad in eBook format. I'm sure it was available in some pirated format, but I'm one of those guys that would rather support the things I want to see more of.