This means Apple, out of nowhere, could soon become the #1 or #2 book retailer in the world by next year. Apple has sold 3M iPads, roughly the same as the Kindle - http://www.businessweek.com/the_thread/techbeat/archives/201...
There will probably be around 2:1 iPads to Kindles and Nooks by the end of the year. They are doing what they did with music with books.