I work 12 hour shifts so I'm on the app for about 3-4 hours a day on my breaks and in the car on the way to work and from work, and it seems to use anywhere between 200 and 350 mb a day that I'm at work (I'm on wi-fi for half the month outside of work). Which gives it about 50-60 mb an hour. Not too shabby considering I flick through songs a lot rapidly which probably eats more data. I do have a 10gb a month data plan so I'm not too worried about my usage.