That is the question Hollywood would once again like the Supreme Court to answer. When VCRs were new Hollywood tried to sue the VCR companies to prevent piracy and lost. The Supreme Court said the studios would have to go after the individuals responsible because there were "legitimate" "fair use" reasons for the creation of the VCR which didn't violation intellectual property rights. You all know the drill, things like back up copies and owning rights in multiple formats. Now Hollywood is going after P2P (or peer to peer) program creators, and once again the issue is piracy of individuals using someone else's technology. The question will of course be: are there any "legitimate" and "fair use" reasons for the existance of P2P software? This is what the Supreme Court will have to decide and depending on the decision the Legislature will have to create investigative tools to go after the "pirates." This could mean the ability to "track" transactions (both with a warrant say or post-transaction) of a suspicious nature. Or require the release of user info.
I personally think the SCOTUS' decision will mirror the Betamax one, I am sure that Morpheus and their kin have some arguments for fair use and I can think of some P2P uses that I think are legitimate. Let's say two individuals writing a novel together need to share files and want constant access or graphic designers, or comic books etc. But maybe not, we'll see.