At the Volokh Conspiracy law blog, Randy Barnett notes, "White House Concedes Individual Mandate is Not Severable".
If so, this could make today's expected court ruling on ObamaCare very interesting, as Thomas Lifson notes in, "Court to rule on ObamaCare constitutionality Monday" (American Thinker, 12/10/2010).
Today's Wall Street Journal has a nice background piece, "Federal Judge to Rule on Health Law's Constitutionality".
If you missed it earlier, David Catron covered some important background information in his 12/7/2010 article, "Of Severability and Sins of Omission".