I think Spotify is in a great position right now, they are building up a huge userbase right now (first step for Facebook etc. too). But the service will monetize very well. For example I would pay extra per album to get to stream a couple albums on the day of their CD release just because it's convenient to have all my music in one application. Or charge me 15$ a month for a gold account and add a feature on the artist page to leave a 1$ tip. This extra 5$ goes into my "wallet" that I can then disperse straight to my favorite artists each month. Like a microtransaction.