eBooks challenge the whole notion we have had of books.
An author can now write several endings to a mystery novel, within a single edition of the "book," and using information about the reader, select which ending to present to a particular reader at a particular time.
A poet could select a specific poem, or group of poems, for a particular reader, based on the time of day, the weather at the reader's location, the reader's demographics, the reader's pulse, the reader's history of past readings and ratings of what he or she has read -- or the reader could turn off the interactive feature and just read the generic ebook.
A minister could select specific Biblical passages, and their order in which to be read, for a particular reader and particular occasion.
On the other hand, authors can't really sign ebooks in quite the same way that they sign hardprint books. (Yes, an ebook can capture a tablet-signature, but it's not quite the same thing, is it?) Book signing tours become something very different in a world in which there are only ebooks.
That they change the notion "you" had of book doesn't mean they actually change anything... *double face palm*...


