More on the Harlan Nomination:
In reading through Tinsley Yarborough's book on Justice Harlan, I came across another interesting passage about whether Supreme Court nominees should testify about how they would decide cases if confirmed. I know that Supreme Court nominees didn't testify in person until Felix Frankfurter, but I have seen a number of suggestions that the refusal to answer questions once called is largely a post-Bork phenomenon.

  Yarborough's book suggests a very different picture. On page 98, Yarborough excerpts a letter from Chief Justice Earl Warren to then-nominee John M. Harlan offering advice on how to testify before the Judiciary Committee. Warren had asked the sitting Justices what advice they would give Harlan, and he reported the results of his survey back to Harlan:
Most of them were of the opinion that if they were in your place, they would not answer questions relative to their views of the Constitution, statutes or legislation. Two of the Justices stated that they would answer very general questions in this field but nothing that was specific.
  Warren recommended that Harlan should refuse to answer any questions about the law, as the Senators were not likely to be satisfied with the kind of general answers a nominee could appropriately provide:
It seems to me that if the Committee attempted to probe your mind on legal matters, it would be for a definite purpose and they would not be satisfied with general questions and answers if the matter was opened up at all.
Yarborough, at 98-99. I haven't looked into the history myself in any detail, but I thought this was pretty surprising.