Originally Posted by derangedhermit
I would add things beyond, for example, ePub 2, such as external links to many types of additional information: author biographies, book commentaries, reviews (and someone mentioned the social aspect).
If you haven't seen the "Marvin" reader yet, you should really take a look. It has really taken ePub 2 to new areas (like what you are talking about here). It is currently for iPad only but the developer has already started on iPhone and plans android after that.
It is hands down better than any other reader I've seen...and free!!