"For every 100 copies of a physical book we sell, where we have the Kindle edition, we will sell 48 copies of the Kindle edition." — NYTimes interview with Jeff Bezos.
I held off buying a Kindle for myself for longer than is normal. The price was the main reason, but I never thought I'd enjoy reading a book on the device.
When my wife finally bought me one for my birthday I started with tech books. The sort of books you burn through and shelve and never read again. Then it was a quick slide into fiction and now I can't imagine lugging a book around that doesn't have a version on the Kindle.