Leaked figures this week suggest Spotify has steep ambitions to reach 50 million users in the US in its first year, partly through integration with Facebook.

Of course, having 50m users is not the same as having 50 million subscribers and the economics of its freemium model require high conversion rates and significant upsell of users to its paid tiers.

In Europe, Spotify has 1 million paying subscribers across seven markets - equal to 15% of its active user base. ...