It still trails the computer-based online audiences of other music services like iTunes and Pandora by a sizeable margin. If it is to catch up with these other services, it will likely be due in large part to the company’s social strategy, which leverages Facebook for social music sharing.
There are some indications streaming music services are getting traction as specifically mobile apps, as well. If Spotify users behave as Pandora users do, they are using the service on their mobile devices.