A Canadian court issued a John Doe order to enjoin individuals that obtained copies of the Half-Blood Prince (from a retailer that jumped the gun) from reading their copies. From IPKat:

Author JK Rowling’s literary agent said

“Copyright holders are entitled to protect their work. If the content of the book is confidential until July 16, which it is, why shouldn’t someone who has the physical book be prevented from reading it and thereby obtaining the confidential information? How they came to have access to the book is immaterial.”

It’s at times like this that the IPKat wishes that he wasn’t such a blackletter lawyer. While strictly the contents of the book may constitute confidential information, the idea of injuncting innocent purchasers in the interests of having a showy launch leave the IPKat frankly horrified.

It seems that it is actually very material how they came to have access to the books. They purchased from an authorized retailer; they are (although not a copyright term) holders in due course, or a bona fide purchaser, as it were. Rowling has a beef, that's for sure, but it ought to be with the Canadian publisher and store, who allowed it to happen.

Let's twist this around a bit and think of what would happen if a similar rule were applied to broadcast regulation, a related legal regime. Would it make sense that you could be allowed to keep a TiVo'd copy of Janet Jackson's wardrobe malfunction, yet be enjoined from watching it ("time-shifting")? Of course not, that's absurd.

Finally, I'm embarrassingly unfamiliar with Canadian copyright law, but I suspect that this next little bit is substantially the same there. Copyright law (at least in the U.S.) isn't about protecting confidential information from disclosure in the first place, it's about retaining control over subsequent use and dissemination. Again, Rowling, etc. have definitely been done wrong, but not by the readers. Enjoining your fans from reading your book can't be such a good idea.