Return-on-Investment in library practice

Many wonder how to account for a place, such as a library, where "what goes into a library isn’t what comes out," to use Andrew L. Pearson's expression.
Here is a book in hand, thanks to Steven Bell, for identifying such an important title: Library Assessment in Higher Education--particularly chapter 5 on assessment of the library's contribution to the educational process.

Question: How do you see the ROI in your library / information practice? Will highly appreciate your response on this subject.

See also:
The Library as Strategic Investment: Results of the Illinois Return on Investment Study, Paula T. Kaufman, University Librarian and Dean of Libraries, University of Illinois at Urbana-Champaign