Spotify's business model is not sustainable. iMeem proved that. MySpace Music is trying to do ad-supported streaming but is bleeding money. Grooveshark is like Seeqpod - it will be shutdown imminently. Ad-supported music doesn't work based on the current monetary asks of the content owners (labels). Ad revenue just isn't high enough.
But don't worry - lots of smart people (and me) are thinking about this problem everyday.
