Agree. I've used iTunes exclusively since, uh 2004 maybe. I was waiting for something like this before I switched. Amazon Cloud Player isn't perfect, but it's pretty great. I uploaded my music library to the cloud (you get 20 GB of space free, and an y music you buy from Amazon doesn't count toward your limit).
From the player, you can also download songs/albums to your phone/Xoom easily, to make sure you have some available when you don't have a 3G or Wifi signal.
The main thing I want from them right now is the ability t shuffle playlists and albums, but for the most part I love it.