Other surveys have found similar results, of course, and this one only covers Norway, but even so: people who download free music (both legal and unlicensed) are much more likely to buy music, too:
In fact, among all 1,901 Norway-based study participants (all of whom were over the age of 15), it was found that those who downloaded "free" music were 10x more likely to download pay music. In other words, music pirates are the music industry's largest online consumers.
It's an awkward problem for the music industry - the people whom it blames for destroying its business are actually the ones who are doing the most to keep it alive. If the IFPI got its dream of throwing all unlicensed music listeners into chokey, it might find that its revenues tank as the former customer base stop buying downloads and transfer spare cash into razorblades, toothbrushes and snout.
[Thanks to Gary W]