If your book is coming out this fall (i.e., Sept-Jan), your website should be up and in perfect order NOW.
Why? Because publishers' fall catalogs are out, and will be distributed en masse at BEA. (I've already received a few in the mail: UNTITLED is a popular name for forthcoming books at Simon & Schuster.) And a poky, amateurish site won't do.
Below are some sites to inspire you; note all the "extras" that hook your attention.