On Monday Amazon announced that over the last 3 months, sales of Kindle books had outstripped those of hardcover books on the bookselling behemoth's website (and that's not even counting free eBooks):
In that time, Amazon said, it sold 143 Kindle books for every 100 hardcover books, including hardcovers for which there is no Kindle edition.
The pace of change is quickening, too, Amazon said. In the last four weeks sales rose to 180 digital books for every 100 hardcover copies. Amazon has 630,000 Kindle books, a small fraction of the millions of books sold on the site
Amazon's reticence to release hard figures has some questioning the statement though, or at least wondering what the figures actually mean given price disparity and books available.
Nevertheless, one interesting point is that Amazon's eBook sales have continued to grow since the release of the iPad, suggesting that while the device may be some sort of rival to the Kindle, it does just offer a new market for Amazon's eBooks (via the Kindle for iPad app).