On the other hand, corporations are already archiving IM communications in order to answer future demands for evidence.

The difference is that telephone usage in the US is commonly expected to not be wire-tapped, while IM is seen as using computers to communicate. In the case of corporations archiving IMs, they own the computers used for IM and they are responsible for what is done with those computers. They also tell their employees that IMs are archived, and to not reveal proprietary information to people outside the corporation, etc.

As for peer to peer file sharing, that was developed to avoid legal responsibility for anything. It is not surprising that the justice system is collaborating with old media to try to bring the technology under legal controls. The judge’s opinion is essentially an opening of a legal debate on what kind of laws apply to peer to peer technology.

Peer to peer VoIP is where this will get interesting…