I just purchased an Android powered tablet that had Kindle for Android already installed. The first book I tried to move to the tablet using Calibre didn't show as being downloaded to the Kindle reader. I checked the files and Calibre had moved an Epub file of the book to the Kindle folder on the tablet. I tried moving that Epub file to the other kindle ebook directory (android/data/com.amazon.kindle) but the reader still didn't find the file. I even tried turning thetablet completely off (powered down) and restarting it. Still no joy. After reading this post, I changed the device options to exclude Epub files, downloaded a book in Mobi format and the reader displays it with all the other Amazon books.
Thanks guys! Even though this isn't a Kindle Fire, your suggestions worked!!!