It's a truly satisfying use for DRM. As a general rule, it annoys me to buy anything which is DRM-limited. Free things, however, are a different kettle of fish. I'm willing to accept some limitations for free. I'm willing to have a "library book" auto-delete after 21 days, especially if I can then "check it out" again later.
Today, I returned all the library books I had out. I wasn't done with all of them, but since I'm not likely to have time for them for a month or two, it seemed safer to just hand them all back for now.
While at the library, I saw posters. "E-books are free!", they said. ("Often, not.", thought I.) "No overdue penalties!"
Back at home, I checked. Yes, they really have. It's a nascent program, not more than around 200 e-books between all categories of fiction and non-fiction, but there are some intriguing options, such as the Rough Guide to Paris. Not that I'm planning on being in Paris anytime soon, but I like knowing I could check out, on a temporary basis, a current guidebook to it and have it take up so little luggage space.
(Whether or not my current e-book software can handle DRM-limited files is a different matter.)