Wow, it's been almost two years since we've seen a report from the LC reference librarian, Thomas Mann.
Here it is: What is Distinctive about the Library of Congress In Both its Collections and its Means of Access to Them, And The Reasons LC Needs to Maintain Classified Shelving of Books Onsite, And A Way to Deal Effectively with the Problem of “Books on the Floor”[pdf]
The Library cannot solve its space problems by adoption of a “digital strategy” without seriously damaging our larger mission to promote scholarship of unusual scope and depth. If the Library’s own access to its own general book collection were to be dumbed down to only the levels of subject access provided by Google, Amazon, or Internet search mechanisms, we would effectively be endorsing, and institutionalizing, the level of ignorance exemplified by the Six Blind Men of India. We would no longer be able to satisfy the information needs of Congress or other federal agencies, or those of advanced scholars, in a timely or efficient manner. It is not enough simply to have comprehensive collections; we must equally have efficient access to them.