If you purchased any Kindle books that are published by Hachette, Penguin, HarperCollins, Simon & Schuster, or Macmillan between 4/1/10 and 5/21/12 on Amazon.com, check your Inbox for a possible credit. Due to a class action suit they have given amazon credit back to customers. You can check your Amazon account for credit here. The credit will automatically apply it to your next purchase of a Kindle book or a print book.
Did you get any credits?