There's a publishing house that works along the same lines for books as Pledge does for music.
Basically the author sets their target costs and a closing date and then people pledge. She can do special offers like a limited run of signed books, maybe a special cover, book with a framed print etc all at different prices. The author is totally in control. If the target is met the book gets published, if not the pledgers get their money back.
I've bought a book from them (Dear Mr Popstar, google it) recently but I can't remember what they are called! When I get a minute I'll go check my emails......