So why can't people just make more copies of books? Here's my thought...
No two books can bear the same title. Why? Because the title is the books Name.
A writer cannot write a book without Naming it.
Not sure how that would work in a practical sense (pages go blank? the story doesn't unfold? or perhaps without expressly Naming it the writer gives the book their own Name) but it does seem to fit the setting concept.
Don't drink the holy-water; we don't like it when you drink the holy-water.
Also, I just started reading China Mieville's "Un Lun Dun", at someone on this forum's request (If I remember correctly). It's some great inspiration, and I'd recommend it heartily.
I also like the spellbook/familiar idea, though I'm not sure how easy it would be (mechanically) to implement. I'm sure it can be done though.
I wonder. Given the power of some of these books to influence/change/warp reality, per M_G's post above, I wonder if the spellbook could actually be a familiar. It seems to me that it would actually be the wizard who would serve in the role of the familiar, and would act as the servant of the book. Through the wizard the book has mobility, enhanced senses, and expanded ways to work it's will upon the world.
Oh ho! I caught the reference. Very sly Fae, very sly.
They'll carry you through the labyrinth with blinding speed. The fastest one, according to rumor, made the Kessel run (from Hobgoblin Spire on the first island to the Jut on the last) in less than twelve parsecs (roughly as long as it takes to make a bad reference).
So I don't know, I like the idea, but I feel it might be a little off here. Opinions?