Peer-to-peer companies such as Grokster and Morpheus parent StreamCast Networks can be sued and held legally liable for the copyright infringement of the people using their software, if the companies actively encourage that infringement.
Some are saying that this may kill peer-to-peer file sharing technologies.
Personally, I disagree.
While it is true that some of these programs (like the original Napster) were designed for the specific purpose of trading music (most of which was distributed in violation of copyright), it is also true that most of the modern programs (like Bit Torrent and various Gnutella clients) are promoted as general purpose file-sharing utilities, not simply music-swapping facilities.
When combined with the fact that these are often used for non-infringing purposes (e.g. several Linux distributions are released via Bit Torrent), I don't think the courts will be able to conclude that the companies actively encourage copyright infringement.