That's what I was waiting for in Ubuntu. You have full integration of the Amazon Webstore. Click and it downloads to your library. Podcasts with Miro-Search click and it downloads, Audiobook support, Internet-Archive search and play. Unbelievable. No separate Amazon-Downloader anymore.
I plugged in my Nexus S and it appeared instantly, ready to drag 'n drop files on it, or set auto-sync. So if you set it to auto-sync, you just can plug in your Nexus S or other Android devices and it automatically syncs you music.It never has been so easy, and I almost doubt it, I will ever see such a simple and great program.
Banshee comes default for Ubuntu 11.04, but can be manually installed on older Ubuntu-versions.
Give it a try. It's free...as in beer and as in freedom.