This is a great idea that could be applied elsewhere as well. For instance, I never know what to do when a node suggests a new feature that I disagree with (sorry tilly). I'd like to be able to '++' the node for being well thought out, well written, adding to the community, etc. but *also* be able to '--' the idea. Sort of an "I appreciate the effort, but disagree with the suggestion" stance.

I've seen at least one instance (can't remember where) in which the author posted an AM followup for people to cast votes on the idea of his original post. This sounds very similiar to what you propose with Book Rankings.

It's the difference between "Good Review." and "Good Book."

-Blake