On a whim, I gave Amazon Cloud Drive a quick test. Launched in 2011, the service promises 5.0GB of free storage accessible from Windows, Mac and the browser.
After a day or so of usage, I've decided I'll be sticking with Dropbox for my for my public documents and encrypted sparsebundles. There are many reasons, but these are the most presient:
The web interface is familiar and easy for people used to Amazon's design language, but its not as slick as Dropbox. It also requires Flash to upload files, in 2013.
The provided Mac client defaults to putting files in your home folder. There's no way to change this in the interface of the application, short of creating a symlink in the terminal.
Dropbox (like S3) can have public folders, with any file placed in it being accessible. With Cloud Drive, files must be individually shared, and a UID unrelated to the filename is created.
It was worth a try, but I feel Amazon has the capability of doing much better.