I spent a good part of my college years in what was then called the Undergraduate Library at the University of Michigan. Getting your hands on a book that was assigned reading for a course was often matter of luck—there never seemed to be enough copies.
Starting in October, the library, now renamed the Shapiro Library, will have infinite copies available, at least of certain books. Using a technology called the Espresso Book Machine from On Demand Books will offer books bound and printed in five to seven minutes. Most titles will cost $10, some shorter books will go for as little as $6.
There a catch, of course. Only books out of copyright are available. So the instant printing will be limited to books published prior to 1923 and books made freely available through other sources, such as the Open Content Alliance.
The Michigan library system has digitized about 2 million titles, both through its own efforts and through work with the Google Book Search project.
UPDATE: The University of Michigan has put up a video of the Espresso Book Machine in action.