Sharing is deemed to be equal to distribution when it comes to copyrighted files. This is very exact actually - why would you want to share something, if you didn't want other people to get it from you? No, you don't actually force people to download it and neither do distributors, so sharing copyrighted files is not right.
In any case, these are not just my ramblings, as a judge from the US sided with the RIAA (Recording Industry Association of America) and ruled that installing P2P file-sharing on your PC is illegal.
So what is P2P anyway? It stands for "peer to peer" and means "from user to user" and means that any side can initiate a session and has equal responsibility. P2P allows Internet users to transfer files directly, rather than through the use of a website or directory. Also, the file transfer is done directly from the users' computers.
I have to agree with the fact that most people that use P2P will have something to do with piracy and infringing copyright laws generally, but it is also used to transfer some large files.
This is pretty important in fighting piracy and properly enforcing DRM. It all goes by the idea of "they won't distribute it if they can't" but I don't know how much good it will do. I mean, before this, it was illegal to download music or movies from other users, instead of buying them, but now, the means of download have been outlawed. I wonder if this is really going to be a hard hit to piracy...
Many pirates have been arrested, a lot of sites and programs have been taken down, but still, if I want to search the web for an artist's album, I'll find thousands of illegal copies of it. If the piracy rate drops 1% because of this new law, then they've scored one point! There is still much to be done, I believe.