Multiple studies have been done on the people who pirate music, and they've found that, on average, people who pirate buy more music than people who don't. That makes sense, if you stop and think about it, because music has a very high replay value. I discovered one of my favorite bands, We're About 9, when my friend Merav gave me a mix tape—the oldest form of music piracy—with one of their songs on it: I've since purchased several albums, including the one with that original song. I don't tend to listen to the full albums very often, but every time the individual tracks come up in my iTunes shuffle, I remember that I want to buy more music by these authors. It's music piracy as a form of private radio, and most people—not all, but most—understand that if you want to keep hearing things you like on the radio, you need to support the artists.
Just about everyone I know has at least a few pirated songs. I recently acquired a pirated copy of Freddy's Greatest Hits, a parody album featuring none other than Freddy Kreuger himself. It's been out of print for twenty years. I do not feel any shame about listening to this rare treasure from the horror graveyard...although I'll definitely buy the actual album, if I ever find it.
Book piracy is different, because the way people interact with the media is so different. According to my iPod, I've listened to the Glee cover of "Don't Stop Believing" over two hundred times. Two hundred times. Of course I paid for it. That song is part of the soundtrack of my life now. Looking at my bookshelves, the single book I've probably read and re-read the most times is Stephen King's IT, where I lost track at eighty. I'm a dedicated re-reader. I re-read IT at least once a year, and frequently more often than that. And I'm only up to eighty. Many people don't re-read the way I do, and very few people re-read immediately. So if I download a torrent of the new Ikeamancer novel, I'm pretty unlikely to run right out and buy myself a copy...and if I want to re-read the book six months later, I may just dig the file out of my hard drive, because it's there. Never underestimate the power of instant gratification.
Past experience tells me that this is the point where someone says "Does that mean you hate libraries/people who loan their books to friends/used book stores?", and the answer to all these things is the same: No. In all of these cases, someone has bought the book. In the case of libraries, the number of copies purchased by a given branch is determined by the number of people who request the book, or check it out once it's in the system. Yes, ten or twenty people may get to read a single copy, but with a pirated book, that number is a lot higher, and that initial sale may not have happened. If I loan a book to a friend, the book comes with a high recommendation ("Here, read this"), and even if my friend doesn't buy their own copy, we're looking at one sale for two people, not one sale (or one OCR of a library copy) for some unlimited number. Even used bookstores are limited by the size of the print run, since they can't get more copies than were initially sold, and are thus a vital part of building the readership for ongoing series. They're part of the natural ecosystem.
People complain about how slow some publishers are to adapt the e-book format, but honestly, the concerns over piracy are a really, really big deal, just because of the impact it can have on a book's overall sales—especially for a beginning author. No, I'm not saying that best-selling authors somehow "deserve" to be pirated, but piracy is likely to be a much smaller overall part of the book's footprint. Dan Brown is not going to be told not to write another sequel to The DaVinci Code over piracy. The author of the Ikeamancer books...might.
Publishing is changing. E-books are, and will continue to be, a big part of that. But unless people remember that book piracy isn't exactly the same as music piracy (and hence culturally viewed as "try before you buy," but almost always leading to that eventual purchase), they'll also continue to be a problem.