"Note: The Cloud Drive Sync application (formerly, the "Cloud Drive desktop application") is no longer available for download. If you already have the application installed on your computer, you can continue to use it. However, if you uninstall the application, you won't be able to reinstall it from the website."
I tried using the unlimited photos service with my prime account and auto-phone-photo-backup service. It works great when uploading or browsing your photos online, but once you go to download your photos, it's one by one.
http://www.amazon.com/gp/help/customer/display.html?nodeId=2...
"Note: The Cloud Drive Sync application (formerly, the "Cloud Drive desktop application") is no longer available for download. If you already have the application installed on your computer, you can continue to use it. However, if you uninstall the application, you won't be able to reinstall it from the website."