I think I recall seeing something on 48 Hours about someone being able to see other peoples tax returns using Bearshare. People unknowingly set up their entire hard drive to be shared using Bearshare, and this guy simply typed "tax" into the Bearshare search engine and he was able to see other people's tax returns that they had filed electronically if they were using Bearshare too. I guess theoretically if you don't know what you're doing when using any P2P software you can end up sharing your entire hard drive. So just BE CAREFUL!!
The thing about P2P is that if you don't own any of the material you are downloading from someone else, or if they don't own it to begin with, you are in direct violation of applicable copyright laws governing such things as intellectual property or music and video productions. In other words, if you haven't bought it, you don't own it and you are breaking the law. Even if you did buy something and then share it with everybody else you are still violating copyright laws because you are only allowed to make one backup copy of whatever it is you bought and you are not allowed to distribute it in any way, shape or form. The P2P software is not illegal per se, but it is facilitating in the illegal transfer and distribution of copyrighted materials.