This is about one of those "enhanced ebooks", more like a multimedia thingy,
http://www.mediabistro.com/galleycat...r-ebook_b26609
But I like the idea of discussing a book from within the book. This could be very useful in academia I think, where an instructor could assign a few pages and then ask the class to write a few thoughts and then everyone's thoughts would simply appear alongside the text, it will definitely change the reading experience. The next step would be to actually alter the text in realtime I guess.