Apple is adding roughly 500,000 new iTunes user accounts every single day, according to analysis by Asymco's Horace Dediu. By that count, Apple will add at least 100 million new users by the end of 2013.
Dediu also calculates that each of the existing 575 million users spends on average $40 a year, which is numerically down on 2009's figure. The numbers confirm exactly how important Apple's iTunes user base is, and explains why it's making an effort to introduce new services like iTunes Radio and gaming peripherals for iDevice casual gaming.
The data also underlines why Apple may be considering introducing its own mobile pay system in the near future—the iTunes customer database may constitute a perfect payment vehicle.