A recent study has suggested that users of popular P2P solutions actually buy more music. I suppose no matter who wants to deny it, the try before you buy method really does work.
When assessing the P2P downloading population, there was "a strong positive relationship between P2P file sharing and CD purchasing. That is, among Canadians actually engaged in it, P2P file sharing increases CD purchases." The study estimates that one additional P2P download per month increases music purchasing by 0.44 CDs per year.