Amazon reports that kindle books have been outselling hardcover books. For every 100 hardcover books sold, there are 143 kindle books in the past three months. This is accelerating too. This past month, for every 100 hardcover books sold, Amazon has sold 180 Kindle books.
Part of the reason for the shift has been changing habits but also another reason for the trend has been the price cuts on the Kindle. Kindle started out at $259 but is now down to $189.