I've had this on my mind because Amazon is the leader in ebooks and 60% of my sales come from them. There, I've exposed some personal information.
I like Amazon. What they've done to change the landscape of publishing is a boon for everyone. They gave authors a choice of not having to live with publisher rejection and readers a wider array of books to suit their tastes. What's not to like?
What I have to say is only my opinion and my personal preference.
I do not believe that the Select program is good for all books, but I have seen how it has helped some authors. To be part of the new Kindle Unlimited ($9.99 monthly fee for all the kindle books you want to read, as far as I understand it), an author has to opt-in to say that Amazon will have their book exclusively for 90 day periods (after which they can pull them out).
As I stated above, Amazon brings in about 60% of my sales currently, but my books are available across multiple retailers. If I pulled them all to go exclusive with Amazon (a requirement to enroll in Select), I'd be cutting off a lot of potential readers. I like Barnes and Noble--my kids and I shop there on occasion and I also have a Nook. I have a Kindle too, plus smartphone, tablet, laptop, etc. on which I can read books from any retailer I want using their software or Adobe Digital Editions.
As an author, I don't have any intention of cutting off 40% of my readers and potential readers just because of a deal at one that may or may not increase my sales, particularly when it involves a flat, shared amount. My books range in price from $.99 on up to $9.99 (omnibus edition of Dark Angel Chronicles). I'd either be cutting off my income or increasing it, depending on what price a particular ebook is. For shorter works, I can see the benefit of being exclusive, and in that I may try it on the Adronis books.
And I'll bet a lot of authors will be considering the same thing. I can see the KU program becoming a short-story to novella mixture rather than novels that could be making more outside of the program.
As a reader, I don't read enough to make $9.99 a month worthwhile. I tend to read more nonfiction and, due to the nature of what I've been studying, I like to have the print book on hand for that. I rarely buy books by the big publishers. If I read one or two indie books a month at $2.99-$4.99, I'm better off paying the individual rates for the books and saving a few bucks, plus the authors earn more. However, If I was interested in reading something from big publishers, $9.99 for unlimited books that normally cost that much or more would be a sweet deal. Throw in a few indie books on the side and I'd still be coming out ahead.
KU can be a benefit to some or a money sink to others. Consider the cost-benefits to you as either an author or a reader, or both.
With it just unrolled, I think a lot of people will give KU a try and many authors not in the program may suffer a slump in sales for a few months, and going into end-of-summer and fall, that's a terrible time for a slump on top of the usual slump. I cringe and wonder how bad it will be but I also realize that some people will realize that it isn't worth their money, as the books they want aren't included or they aren't reading enough to justify the fee. Yes, I try to stay optimistic, but I've also been wrong.
There are no absolutes for authors or readers. As an author, we have our readership and financial situations to consider. As a reader, it's an economic and selection choice.