Spotify's advertising promotional materials sent to AllThingsD reveal the European streaming music service is ambitiously planning to snag 50 million users in its first year of operation in the US. The company is touting its partnership with Facebook as a big contributor to this number, with 150 million Facebook users getting invitations to sign up for Spotify. The company is also promising advertisers will be able to build music apps on their sites and on their Facebook pages.
