Wired is running a story that links the size of e-readers to sheep. I think it is a stretch (and they admit it, as well), but the story does have a terrific guide to why books have traditionally been their various sizes… and it does have a lot to do with sheep:
The Hidden Link between E-Readers and Sheep
The Wired article was inspired by a post on the Got Medieval blog. I like the look and feel of vellum, although it is a bit squeem-inducing to think about what it is made from.