You can listen to Audible audio books on your Sansa player by supplying your personal DRM access code.
I wonder if it is similairly possible (or desirable) to listen downloaded tracks from your favorite music stremaing service such a Rdio and Spotify? You can usally download your music from those services for offline listenning to you smartphone but we know listening to music on a smartphone sucks.
What do you think? Would it be uselful?