The reader uses an app on their smartphone to take a picture of the QR code, and then the reader is directed to a website that has content related to the paper book.
Did you notice how limited the audience is for QR codes? You have to have a smartphone with a camera. I, for one, don't have a smartphone. You could look at it this way. QR codes are intended to add value to a paper book (by linking to web content). But the value the code adds only benefits a part of the readership. Wouldn't it be better to provide a link (which everyone can use)?
Part of my dislike for QR codes is that they remind me of the Cuecat bar code scanner (from the late 1990's tech bubble). The Cuecat was one of those bizarre devices that only get funded during the hype of a bubble (when everyone has lost their senses). The idea was that bar codes would be embedded in adverts and users would wipe the bar code and be directed to a web site. It sounds a lot like QR codes, doesn't it?
The Cuecat died because people figured out that it was easier to simply type in the URL. And now that URL shorteners are in common use I would hope the same happens to QR codes.
P.S. I'd like to make a prediction about QR codes. Some time within the next year (if it hasn't happened already) you're going to be able to snap a picture of a page of text and then have the contents digitally converted and Googled. Where will the QR code be then? They will seem like a quaint curiosity, IMO.