As with any judicial nominee, Miers must be circumspect in those questions that she does answer. It would be inappropriate for her, as for any nominee, to address what they would rule on any case that might come before them.
So, in my view, she is allowed avoid certain questions, but should fully answer others.
Which to his enormous credit is what Chief Justice Roberts did, with fine discrimination and discretion. I so enjoyed listening to his testimony before the Judiciary Committee!
My husband old me (based on a source I didn't see) that the Chief Justice really "hit the ground running" WRT to the oral arguments in the Oregon "right-to-die" case now before the Court. B. said the "pro side's" attorney barely got three words out before Roberts started grilling him... "But isn't what you are arguing for already illegal?" Or words to that effect.... If B.'s report is accurate, then I think this would indicate that the Chief Justice is rather proactive. :^)
Of course, this doesn't tell us how Justice Roberts will finally rule on this case. It does tell us that he likes to get down to brass tacks right out of the gate.