I think that for the most part Apple has the same streaming contracts as Spotify/Rdio/Pandora/etc.

There are still a number of albums/songs/artists missing that simply aren't available anywhere (Tool and The Great Gatsby soundtrack are two I always check).

But it seems that I should be able to mix tracks I own with streamed tracks, which is going to be the killer feature for me personally.

Having used Rdio for many years now, and Zune Pass previously, comparing apples-to-apples (no pun intended) with will be interesting.