Two legal scholars, Aaron Perzanowski and Chris Jay Hoofnagle, have created a fake e-commerce site called "Media Shop" as a means to study the behavior of online shoppers. They have published their findings in a paper called, "What We Buy When We Buy Now" (pdf). It's a solid read for anyone seeking to learn more about how traditional ownership rights transform in the digital context.
When you buy a book from Half Price Books, you have a pretty good intuition of your ownership rights with respect to that bound stack of pages. Once you've signed the receipt, it's yours to take home. Much like most things you own, it's your personal property, or in 4th Amendment terms, part of your personal "papers and effects." You can sell the book, lend it to a friend, or even light it on fire. Put simply, unless you're copying the book, you can do whatever you want with it sans the rights-holder's permission.
Those commonly held intuitions about ownership begin to crumble when it comes to purchasing things in digital format. A book I buy and store on my Kindle is different from a physical copy in obvious ways: It won't gather dust on my bookshelf, nor will it have annotations scribbled onto the margins. But what's not so obvious is the large chunk of ownership rights you're giving up when purchasing digital, as opposed to physical, copies of books online. (Of course, this is not just limited to books; movies, games, music, and much more also come into the fold.) What's happening here is that your rights to those digital purchases are being continuously filtered through a maze of IP law. Moreover, your rights are significantly limited by the fine print in the Terms of Service that you agree to at the point of sale. More often than not, key provisions are couched in lengthy Terms of Service agreements, and as you might suspect, people generally don't take the time to read through those. (In fact, if it was your full-time job to read all your privacy policies--i.e., 8 hours/day--it would take you roughly 76 work weeks to complete the task.)