Japan seems to be light years ahead of the US when it comes to innovating with digital publishing. In part, that's because text messaging and web browsing via the cellphone took off in Northeast Asia like nowhere else in the world. The latest innovation is to give people who purchase new books access to the electronic version as well:

In concrete terms, this means those who have made a purchase will be directed to a special link on the Chûkei Publishing Homepage, where they will input the last five digits of the ISBN code found on the last page of their book, and a registration number for each volume. Next, they will answer a question which only a person in possession of the book would know, such as, "what is the first letter on the second line of page four?" Then after inputting some basic information such as name, e-mail address and password, they will be given access to the electronic version with functions such as a digital keyword index, memo, and bookmark functions.

Here's the rest of the article. Sounds like something Chin Music should try.