I don't know how widespread this is within their library, but Spotify interests me in the niche music they serve. When I first got the beta, I loved that I could find a few of the more obscure albums of Irish music on there (don't laugh!) However, a few weeks ago, a large selection of these disappeared. I signed in one day, and many of my playlists were next to empty.
I presume that they encountered a rights issue which forced them to withdraw the music. But from an end users point of view, my quality of service was diminished, without prior warning.
Shame really, but the experience was enough to put me off subscribing.