Background information can be found at Opposing Copyright Extension
Information of the constitutional challenge to the Copyright Term Extension Act is here. The case will be argued before the U.S. Supreme Court, probably sometime next term. The outcome is far from certain. Maybe the Court will strike the law down; maybe it will affirm the lower courts' finding of constitutionality, but on other grounds (the grounds on which the lower court found the law valid were pretty silly, and avoided deciding the case on its merits). Or they may send the case back down to the lower courts to be argued on the merits. Or maybe we will see some other outcome. Then there is the question of the breadth of their ruling; a very broad ruling against the Act might have implications for earlier extensions of the term of copyright. A more narrowly-focused ruling might effectively short-circuit a challenge to the 1976 law, or leave open the question of the 1976 law's validity.
A brief and insightful discussion of this case is Chris Sprigman's The Mouse that ate the Public Domain.