MGM v Grokster (and Morpheus) is meant to decide whether tools like Limewire and Morpheus are legal to build and distribute. If the case rules against Morpheus, it could be the end of file sharing software as we know it. Basically, Limewire contributors possibly could be held liable for every infringement made by anyone they distribute the software to, or something like that.

Hopefully cooler headers will prevail.