Further to my opinion that the Grokster decision was not any sort of condemnation of P2P networks, Bob Lefsetz has an excellent post summarizing the decision in his usual eloquent style:

If you’re a heinous motherfucker contributing nothing to society, profiting by inducing others to break the law, you’re gonna be liable. If you come up with a new software program with the intent to improve society via legal uses, and don’t INDUCE others into criminal activity are you liable? PROBABLY NOT!!!

He Includes Justice Souter’s opinion:

[Regarding the services] The point, of course, would be to attract users of a mind to infringe, just as it would be with their promotional materials developed showing copyrighted songs as examples of the kinds of files available through Morpheus. Morpheus in fact allowed users to search specifically for "Top 40" songs, which were inevitably copyrighted. Similarly, Grokster sent users a newsletter promoting its ability to provide particular, popular copyrighted materials.

Well in my opinion stealing music is not on, and that is exactly what Grokster and StreamCast were promoting to its user base. If Sony was promoting the stealing of movies with Betamax in its marketing, and explaining how to improve efficiency in stealing movies with their product, they would have lost their landmark case. The video recorder player thrived, because there was a number of uses that went beyond stealing, even though stealing happened and continues to happen with that product.