September 1st is 7 hours away as of the writing of this post. You will be able to buy a Tree Book version and those who preordered the eBook version should be able to download their copy.
May I suggest that if you plan to buy a Tree Book version, and, in some instances, even the eBook version, that you visit your local Independent Book Store and order your copy there? The Independent Book Stores need your support. Here are the ISBN numbers for each version: eBook ISBN#: 978-0-9814256-6-5 Tree Book ISBN#: 978-0-9869731-7-8. Having this number might make it easier for the Independent to order the book.
You can order the Tree Book version from Amazon, Amazon.co.uk, Barnes and Noble, Exlusive Books (RSA), Loot (RSA), Pulp Books (RSA), Fishpond (Aus) and Mighty Ape (NZ). The links for these locations should be live on, or shortly after, September 1st.
You can also visit Rebel e Publisher‘s site.