Of course most of the noise about what's at stake in this and other Supreme Court nomination battles concerns the hot-button 'cultural' issues: gay rights, abortion, etc. That's understandable: passions are high, motivated constituencies are well-formed, and the issues are clear, at least on a emotional level, to a wide swath of the public.
A couple of conservative nominees will of course, cause progressives headaches on all these issues, and with enough time reverse a lot of important gains that have come through the courts. But even more damage can be done if the Supreme Court starts chipping away at the federal government's authority to make laws for all states. There has already been some movement in this direction under this court, but another justice à la Thomas would firm up the anti-federalist block, and put 60 years of laws at risk.
So it is certainly good news that Senator Arlen Specter, the Republican Chair of the Judiciary Committee, has decided to bare his moderate chops and demand some answers from Roberts on his thoughts about how far Congress's authority to regulate interstate commerce ought to go. I have little doubt that Roberts will say the right answers. But at least he'll be asked the right questions.