As books goes digital, Amazon is managing the transition nicely with the Kindle. Amazon now sells more Kindle books than print books , and offers nearly a million ebook titles. In a research note that just went out this morning, citi analyst Mark Mahaney estimates that sales of Kindle devices and digital books will account for 10 percent of Amazon's revenues in 2012. Thanks to the Kindle, Amazon's U.S. book business is growing faster than at any point in the last ten years. So far in 2011, Amazon has sold three times as many Kindle books as during the same period last year.