Theoretically (under american law) provided the software has a legitimate use then there is no legal justification for shutting it down (even if many or most users use it for illegal activities).

One of Napster's problems was that it had central servers that held details of the files available on the network. These central servers could be (and were) targetted by legal action, thus effectively shutting down the network.

Gnutella is truly peer-to-peer. The client developers are in no way acting illegally in that they do not serve or hold lists of copyright material (Doesn't mean that somebody won't try to sue them - just that they won't have much of a legal leg to stand on).

Any individual user on the gnutella network may find themselves under legal scrutiny if they are sharing files that they do not have the copyright holders permission to distribute. But in a true p2p network (napster wasn't) the loss of one host/client will make little difference to the others.

Mark