I have to thank Nigel Mitchell for this link to a story about authors complaining about Kindle Unlimited. Kindle Unlimited is the program that allows users to pay $9.99 to get as many books from Amazon's Kindle Select Program as they want. Basically it's Netflix for books. There are already services like Oyster that do the same thing, though I looked at Oyster and its selection kind of sucks.
Anyway, I've already gone on record as saying Kindle Unlimited has been awesome for me. It has just about doubled the money I get every month. Sure I might not end up getting as much per book with Unlimited, but would the people who get it through Unlimited actually buy the book otherwise? Or would they buy it and then "return" it since Amazon's system is so pathetic about returns?
In reading the article, I think the people who are complaining are those who are having success beyond Amazon. If you're considering whether or not to enroll in Kindle Unlimited that's what you need to consider. If you've have good success with other sellers like Smashwords, B&N, or Kobo then you don't want to use Kindle Unlimited because you have to take your book off sale from anywhere except Amazon for three months at least.
If you're like me and 95% of your sales are coming from Amazon, then Kindle Unlimited makes sense. With it I can double my revenue stream and people who might be on the fence about spending $2.99 for a 50-page book or considering doing something shady might not if they think they're getting it "free" with Kindle Unlimited.
As for whether Kindle Unlimited will change the world of bookselling and so forth, it's really too early to tell.