I'm a paralegal so I'll share my perspective on this ruling.
It means, essentially, that filesharing (P2P) providers are now held liable for copywrite infringement because they provide the tools necessary to locate and share media.
They always existed within a legal loophole. Since they did not PROVIDE illegal material, only allowed individuals to share amongst themselves, they got away with it.
An appropos analogy;
You know a drug dealer.
You know a junkie.
You introduce the two of them, for no specific reason.
The drug dealer is now selling to the junkie (illegal).
What the hypothetical 'you' did in this scenario was perfectly fine... albeit negligent. It wasn't a crime.
So this ruling would, based on the aforementioned analogy, mean that you could be charged with a criminal offence simply for allowing those two people to meet.
Now, back to the topic at hand... this means that programs like Kazaa, Soulseek, Morpheus, Napster, etc (P2P client-based programs) can all be held liable for copywrite infringement, even if they aren't HOLDING any illegal material. I means they will likely all be shut down, or become 'pay for legal media' services instead.