Looks like E-Books are headed in the same direction that MP3's did a long while ago - dominance over the dead tree format. Amazon just released this:
By July 2010, Kindle book sales had surpassed hardcover book sales, and six months later, Kindle books overtook paperback books to become the most popular format on Amazon.com. Today, less than four years after introducing Kindle books, Amazon.com customers are now purchasing more Kindle books than all print books - hardcover and paperback - combined.
The publishing houses are about to go all RIAA on us, I expect.