I myself can't laud the P2P apps for expanding my horizons, but I can definitely say that the "old school" days of being on EFNet's #mpeg3 IRC channel got me into a lot of new music. Not just by talking about music with others and asking what's good, but also when I'd go onto someone's FTP site. I'd be looking for certain things, but a lot of times I'd throw in some other songs to my batch download that I didn't really know about, but happened to be available. With the P2P apps, you're usually searching, whereas the FTP sites allowed for more of a "browsing" type approach.