Mark Dain
Availability is good; whatever is on the iTunes store you can listen to. Quality -- If you're talking abou the file, the quality is iTunes, which has always been great IMO. Usability? It's Apple; it's very usable. As for reccomendations, it's now at the point where a good friend (with a good taste in music) is reccomending music to me. It recently pulled an album I used to listen to as a kid. Got a lot of nostalgia as well as rediscovering a great artist. Also it works across many genres; it won't get messed up if you listen to country, then heavy metal.