You kids today. In my time, we had to read books by hand. Using our fingers to turn the pages. Video? Audio? Pah! We made video and audio in our heads! Sometimes we got a stuffed animal with the book, and ya know what? We were happy! You're just spoiled, the lot of you. Get off my dang lawn!
All old-fartness aside, there does seem to be a rise in the number of books that have multimedia components--not merely tie-ins, but necessary elements to understanding and following the story.
Scholastic's 39 Clues series was in the nature of an experiment, but it's an experiment that a number of other publishers are trying as well. Check out this story on multimedia publishing over at Publisher's Weekly for more.
What think'st thou? Of course, it's all about the almighty dollar, but are publishers pandering to increasingly fleeting juvenile attention, or are they capitalizing on the new literacy?