There haven't been any moves to crack down on these exchanges (other than the requirement that the Kindle Lending Club rebrand). But now it appears that Amazon has shut down one such site, Lendle. The company's website went down briefly today, and Lendle tweeted that Amazon has revoked its access to the API.
We have contacted Amazon for more details on the decision, but the company has not responded at the time of publishing.
According to Lendle, Amazon restricted access to the API as the lending network did not "serve the principal purpose of driving sales of products and services on the Amazon site." Like many of these e-book lending startups, Lendle is an Amazon Affiliate member and does get a cut of the Amazon sales generated via links on its site. That "Buy Now" option is pretty important as you can only lend a Kindle book once and only for two weeks. Add to that very few publishers make their titles available to lend, it's hard to see how Lendle, or any of its competitors, doesn't in some way drive more book sales.
A more likely reason that the API access was revoked is that Lendle ran afoul of some other aspect of Amazon's Terms of Service. Lendle did pull a list of a user's entire Kindle library (lendable or not) for example.
Lendle says that, "It's sad and unfortunate that Amazon is shutting down Lending sites." But at this time, it appears as though it's Lendle and not lending that is the target of Amazon's ire. Other e-book lending sites - eBook Fling and the Book Lending Club, for example - remain up and running.