I'm not really sold on the idea that we need interactive textbooks, I've never had a textbook that wasn't very sufficiently searchable using the contents and index, and I don't see how you can keep a straight face and make the argument that a $400+ iPad is more durable than a $30 textbook, especially in a school environment where some textbooks can last for a decade or more.
Apple may want the iPad to be the standard with all their little monopolistic heart, but I just don't see it happening anywhere but in random charter or magnet schools who want to show everyone how hip they are with the new technology.
Why the hell would you WANT your child using a Textbook that's a decade old or more? That's part of the problem. When I was in high school (94-98), I had a social studies textbook which had a giant "USSR" label over the northern Asian continent.