Let the hive mind of Engadget get that for you.
"I am looking for a device that will stream sound from one source to several recipients. For example, I want to stream sound from my TV or stereo to my phone or MP3 player that has radio and Bluetooth capabilities. I have looked into radio transmitters and they seem like a decent choice, but I can't find one that uses external power (USB or from the plug) and I would want one with a transmit range of around 50 meters. Thanks!"
I'm pretty sure you can back them up just like iTunes purchases.
But the "near DVD" picture quality of iTunes SD content would make spending 15 bucks awfully hard when a better quality SD DVD can usually be had for about the same price at Best Buy the week of release.
Not to mention the DRM issue. What happens when iTunes is not longer at the top? Google Video and MSN music were warning signs that "buying" doesn't really mean "buying" when DRM is involved.
Personally I think its a bad idea to build any kind of library around a proprietary box. If Phillips or Panansonic goes out of business I can always buy another DVD player.