So some of you who preordered your books have gotten them and some of you haven't. There are a couple explanations for this based on Amazon's patterns of shipping, (1) the book isn't technically published until September 1st, so Amazon isn't obligated to ship the book yet, (2) they ship whenever they want because they're Amazon, and (3) they ran out of books. All three are probably true. Amazon.co.uk is definitely out. Amazon.com always claims to have more copies than they do, figuring they'll get their hands on the copies within a reasonable amount of time unless a huge amount of orders come in all of the sudden. So "In Stock" doesn't necessarily mean that, it just means, "We probably have it and if we don't we can get it real quick like."
Barnes and Noble and some other major book stores got their copies last week, and put them on the shelves, which is called a "staggered" placement. Independent bookstores generally don't put things on shelves until the publication date.
The long story short is that the book sold out. More precisely, it was vastly under-ordered and went to a second printing before the actual publication date. So I want to thank everyone who ordered it; hearing that I went to a second printing was the best news I could have possibly gotten on my birthday, and I did get it on my birthday (Aug 28th). I still don't have my Amazon order. I don't have my author copies either, because they were shipped to my agent's office and she's on vacation. So I had to go to Barnes and Noble to buy a copy of my own book - which I have to admit, was kind of cool.
Second printing is different from a second edition. An edition indicates the book has been altered in some form, a printing is simply another run of them turning on the machines and producing more of the same. So, the second printing will be exactly the same book.