As I've said, I'm trying to keep an open mind, but I won't really feel completely comfortable until some DS fan whose opinion I trust reads the book and also thinks Grahame-Smith could be capable of coming up with a great script...
Before Grahame-Smith was attached to the DS film, David Selby was asked to write a piece about the book based on his own interest in/writing on Lincoln and I assume also his association with the horror genre through DS. Unfortunately, I don't have the specifics on when and where it will appear.
FWIW, I kind of liked the book, but
[spoiler]I am also a bit uncomfortable with S-G's need to try to make slavery worse somehow for the purposes of his story. The reality was bad enough.[/spoiler]
The premise of the book seems over the top, but he approaches it very seriously, and, when you think about it, isn't that DS in a nutshell?