Currently Apple sells approx. 1.25 million songs a day, and the company expects to sell about half a billion songs annually.
Steve Jobs, Apple CEO, was announced his surprise at the scale of the figures, commenting today "when we launched the iTunes Music Store we were hoping to sell a million songs in the first six months - now we’re selling over a million songs every day, and we’ve sold over a quarter billion songs in total."One of the driving forces behind the success of Apple's online music store is ofcourse the iPod, which takes use of this service.
Source: NeoWin