I am a big fan of Amazon and I tend to buy all of my music from them, mainly since they were the first to offer legitimate music downloads without DRM.
I hit a snag. Now that we are surrounded by “the Cloud(tm)”, Amazon will store your purchases so you can always get them, but the bad news is they want you to use a piece of proprietary software called the “Amazon MP3 Downloader” in order to get them to your system.
For Ubuntu, they only have a version that was written for 9.06 and only in 32-bit mode. I am running 12.04, 64-bit and I got a lot of errors trying to install their .deb.
Hunting around I came across a way to deal with this. When you try to download the files from the Amazon Cloud you will be prompted to download the Amazon MP3 application. In small print under that should be a “click here if you have already installed it” link. That sets a cookie on your machine that will allow you to download the .amz file which is needed to access your mp3s.