Very good primer on the issues in the Viacom vs. YouTube case:

For most of the history of copyright law, it was Congress that was at the center of copyright policy making. As the Supreme Court explained in its 1984 Sony Betamax decision, the Constitution makes plain that “it is Congress that has been assigned the task of defining the scope of the limited monopoly,” or copyright. It has thus been “Congress that has fashioned the new rules that new technology made necessary.” The court explained that “sound policy, as well as history, supports our consistent deference to Congress when major technological innovations alter the market for copyrighted materials.” In the view of the court in Sony, if you don’t like how new technologies affect copyright, take your problem to Congress.

The court reaffirmed this principle of deference in 2003, even when the question at stake was a constitutional challenge to Congress’s extension of copyright by 20 years. Challenges are evaluated “against the backdrop of Congress’s previous exercises of its authority under the Copyright Clause” of the Constitution, it wrote. Congress’s practice — not simply the Constitution’s text, or its original understanding — thus determined the Constitution’s meaning.

These cases together signaled a very strong and sensible policy: The complex balance of interests within any copyright statute are best struck by Congress.

But 20 months ago, the Supreme Court reversed this wise policy of deference. Drawing upon common law-like power, the court expanded the Copyright Act in the Grokster case to cover a form of liability it had never before recognized in the context of copyright — the wrong of providing technology that induces copyright infringement. It announced this new form of liability even though at precisely the same time Congress was holding hearings about whether to amend the Copyright Act to create the same liability.