"I still wonder if more libraries should experiment with patron-driven selection—point our users to millions of available books, perhaps through a mash up of information cobbled from WorldCat, Amazon, publishers, book jobbers, etc., then a user could actually purchase (or libraries could even lease access to) an item only when a user expresses the interest or need to use the full text. While we’re at it, let’s let them decide what format they prefer: p-book, e-book, audiobook, etc. …"  "The Long Tail Wags The Dog"  ALA Techsource.

This ties in nicely with my food stain theory of acquisitions — First, Open the library to food and drink. Second, Track the occasional spill on our books.  By spilling, the patron inadvertently "marks" the in-use item – It is a defacto statement of utility.  Upon spotting the stain, we should, as a rule, acquire a fresh copy and/or newer edition of the damaged item.