According to a Norwegian study, those who downloaded free music, either legally or illegally, purchased ten times more music than people who did not download free music. Billboard recaps a story in Afterposten. The study followed 2000 people over the age of 15.
This points to what I always believed, that serious music lovers will always purchase music. I think a lot of people download music to get a preview of what they will purchase. The few seconds you can sample on iTunes is not enough to judge. How long did the major labels release albums with one hit and 9 inferior songs without the option of buying just the single? The music consumer got fed up with it. They got hip to the lousy music. Wonder why the single is king now?