Back in the day (~ 2000) when Napster a going concern I downloaded hundreds of songs and never bought a CD.
I think subscription based services are the best these days, like Zune Pass. Then you can try before you buy. I have bought a few CD's since being exposed to them on the Zune marketplace I would not have purchased otherwise.
Sweet Jesus, what does Microsoft get in exchange, will they have control of the ads placed on facebook? Mind you I've never been to facebook I assume they have ads.