Here is an interesting study by the American Assembly at Columbia University , summarized in the chart below.
Fundamentally it shows that the very people who pirate music online are also the people who buy more music through legitimate channels. Looking at the data it makes sense -- people who love music get it any way they can, legitimate and/or pirated; people who don't care about music obviously don't care about pirating it either.
I suspect the same pattern is true for e-books.
But it does pose a cautionary tale for the recording industry when they go after music downloaders -- they may well be persecuting/prosecuting their own best customers, which might not be such smart marketing.