They have most of the albums from the mainstream DJ's, but once you start going into the more obscure stuff it's hit or miss.

Like they have Nicolas Jaar's new album, but not much stuff from Enhanced Recordings.

The windows 7 app is actually the OS's music player. There's a service called Zune Pass where you can stream/download unlimited songs per month for $15, and keep 10 forever.

I have this for my current Zune and IMO it's the best value in music distribution. It's so much better than paying for individual tracks or albums.