Pandora's revenue contribution to the music industry

I was thinking as I was running today about how much I love Pandora. My thoughts turned to why I love Pandora and the best word to describe why is "discovery." Pandora helps me discover new music. It's the discovery process that I love the most. I then started thinking about how the music industry has benefited from Pandora's discovery. Has anyone done any analysis on how much new revenue Pandora has contributed to the music industry? I realize Pandora can track the click-throughs on its buy button or iTunes or Amazon buttons and then track how many convert into sales but so many times I've purchased a song off of iTunes by directly searching. Pandora has no ideas that it was their discovery that caused a new sale. So I'm curious. Any estimates or thoughts out there?