Through a mysterious glitch in the Amazon Kindle Store, all the buy buttons on Kindle eBooks were deactivated this afternoon. UPDATE: The problem has now been fixed.
In the Kindle Forums, user Duncan Lockhart posted a message from Kindle Direct: “We are currently working on a website issue that is affecting the buy box for Kindle books. Some Kindle books are not displaying pricing information and show as unavailable. We anticipate the issue will be resolved shortly, and will update the network when it’s been fixed.”