It's a measure of how entrenched I've become in Kindletopia that this option hadn't occurred to me. The main reason I moved away from paper books was because the the sheer space they take up in my house. Five of us live in an okay-but-not-massive house and I read over a hundred books a year. There just isn't the space to have them all hanging around. But if the whole point is to give the books back in a couple of weeks...
Essex Libraries have an awesome online reservation system - if the book you want isn't in your local library they'll have it sent over from another library in the county. Fifteen minutes later I had the following beauties winging their way to my library from such exotic locales as Canvey Island and Basildon.
All hail Essex Libraries. In a time of massive local government budget cuts, you are still being awesome.