Apple announced today that Windows users have downloaded more than 1 million copies of iTunes Windows in the first three and a half days since its launch.
Furthermore, over 1 million songs have been purchased at the iTunes Music (presumably by both Mac and PC users) store over the same time. In comparison, the iTunes Music Store sold one million songs over 7 days during its initial launch on the Mac in April.
Steve Jobs revealed at last week's Music Event that Mac users alone were purchasing music at a rate of 600,000 songs a week.