Since it is a book about grammar, I'm taking my time to look over it carefully and make sure there are no mistakes. It would be incredibly embarrassing for the book to go to print and then for us to discover that there's a misplaced comma or a word spelled incorrectly (can you imagine?). There is no spell check accurate enough for this.
The release date is still set for September 29, 2009, and you can pre-order the book on Amazon. Go ahead and do it. You know you want to!