People who download music from Peer-to-Peer sites buy 30% more music than people who do not

"US P2P users have larger collections than non-P2P users (roughly 37% more).  And predictably, most of the difference comes from higher levels of ‘downloading for free’ and ‘copying from friends/family.’
But some of it also comes from significantly higher legal purchases of digital music than  their non-P2P using peers–around 30% higher among US P2P users.  Our data is quite clear on this point and lines up with numerous other studies:  The biggest music pirates are also the biggest spenders on recorded music.
Our German results appear to confirm this finding–in fact, extravagantly so.  German P2P users buy nearly 3 times as much digital music as their non-P2P using peers.  We qualify this because the German results are based on too small a sample to be statistically reliable: only 4% of respondents (39 people) reported using P2P networks.  Yet the results are consistent with our wider findings.  German P2P use is mostly the province of digital music aficionados who download in large quantities and who also buy in much larger quantities than their non-P2P peers."

Source:  American Assembly, 15th October 2012

Note - lots of other interesting stats in the report, inc the fact that the median person aged 30-49 has only 30 albums worth of digital music