Just received a notice, from smashwords, that the early book sharing sites, Flikart and Oyster are now belly up. (Oyster was purchased by Google, which is shuttering it, which means they're likely to launch their own service soon to compete directly with Amazon since Google Books (the sales site) is performing so badly).
This shows that Amazon has essentially captured the entire book share enterprise, and smaller entities can no longer cope on an independent basis. Although I've never sold much on any of these platforms, and refuse to participate with Amazon's platform which discriminate against larger books (i.e. those over 10,000 words), it's sad seeing book selling options shrinking.