I heard Lessig talk here in Austin a few weeks ago and he said at that time that he expected Section 512's fundamental deal, not just the subpoena provision, to be attacked by the content community in the next year. He also cautioned that the ISPs were not as organized on this issue as the content industries were, and he thought it possible that basic limitations on liability could go down unless they did get organized. In this NY Times Op-Ed piece, Make Way for Copyright Chaos - New York Times, he notes that not only can the battle take place before Congress, but increasingly, before the Supreme Court. That's what Viacom is asking the courts to do: adjust the deal that everyone was happy with in 1998, but that Viacom no longer likes today.
What seems equally disturbing to me is that these are pretty brutal tactics for what was fundamentally a negotiation of the relative values of content and promotion on the Web. This is all about a business model, probably one that won't even be relevant in a few years given the fast pace of change online.