At the end of 2014, artists like Taylor Swift pulled their music from Spotify citing inadequate compensation and music being made available to non-subscribers free of charge. Those vocal lashings didn't stymie growth though, as the streaming service has added 2.5 million paying users since November, bringing its paid tally to 15 million. During that time, the total user count grew to 60 million -- up from 50 million in two months. What's more, the growth is accelerating: It took about 17 months for Spotify to move from 5 to 10 million, but roughly half that time to hit 15 million. This means that only a quarter of the company's active users are paying customers, a percentage that's remained consistent for a while now.