Wow, quite a disparity in the impressions of "King's Indian Battle Plans!" I guess different people are looking for different things in a book like this.
I just received my copy of the book in the mail about 2 weeks ago, and I've only made it through about a third of the book (it's a big book!). Still, I thought I'd weigh in with my opinion.

First, I don't want to hurt IM Martin's feelings (and probably won't), but there are some problems with this book as a purely theoretical work. Some of the analysis is dated, some of his conclusions are rather subjective, etc. So don't buy this book if you are looking for an up-to-date, perfectly objective theoretical summary of the entire King's Indian. (Not sure what book you would buy though. Maybe there has been a recent ECO published on the opening. But ECO pretty much sucks these days....)
Second, and notwithstanding the first point, I think this is a wonderful book! It is simply chock full of ideas (or "Battle Plans," if you prefer) and great games, the vast majority of which are well-analyzed and placed in their theoretical context. (I think I remember someone stating in this thread that this book was something like a database dump. This is pure nonsense. There has been a lot of work put into this book, and it shows.)
I played the King's Indian as my main defense to 1.d4 in the late '80's and early '90s at the master level, and having gone through just a third of this book I feel that my understanding of certain lines and typical positions and their possibilities has improved substantially. (Of course, I never really understood it that well when I played it, a fact that was reflected in my rather poor results with the opening.)
I can't really speak to how much of this book is reflected in IM Martin's previous work on the ChessPublishing site, as I haven't done a comparison. However, there are obviously substantial additions due to the dates of the games (there are a lot of games from 2003 and some from 2004 in the book). And having all the material in a physically attractive book (which I think this is) is very convenient. But it has over 240 annotated games (with a lot more without annotations in the notes)! It's a massive book, full of interesting stuff, some of which is already on ChessPublishing. So what? I just don't understand the complaint about duplication.
Thirdly, I think this book and most of the advertisements for it are pretty much up front about what this book is intended to be. It is a book of ideas, as played in many absorbing, dynamic struggles between strong players. Sure, if you're wondering what the latest theory on the Shirov exchange sac in the Bayonet Attack is, you won't find that here. (You will, however, find twelve nicely annotated games that will probably improve your understand of the ideas behind the Bayonet Attack.) But that kind of theory is changing all the time, and every book on the King's Indian will be somewhat out-of-date by the time it is published. (That's why you subscribe to ChessPublishing!). I highly doubt that any player below, say, IM strength, could go through this book seriously and not significantly improve his or her understanding of the King's Indian. And understanding is more important than knowledge of up-to-date theory; or rather, without understanding such knowledge is virtually useless.
I have sort of a love-hate relationship with the King's Indian. As mentioned above, I had a fairly miserable record with it when I played it, compared to how I was doing in other openings. At the same time, I beat a few IMs pretty badly with the opening, mostly because the King's Indian is like that, and when things go wrong for White they tend to go terribly wrong. And there are so many wonderful games in this opening! Not just the games where Fischer or Kasparov rolled some fellow world-class GM, but the games between regular GMs and IMs as well, which are often full of tension and dynamism. One of my most vivid chess memories is participating in the post-game analysis of King's Indian game in which GM Stefan Djuric (as Black) had beaten a local master, a game in which Black's attack seemed to come out of nowhere and then continued on for some 20 moves. Again and again in the post-game analysis Djuric would refute our suggested improvements of White's defense with these simply amazing sacrificial lines.
Finally, you could also just view this book as a collection of such games, and (for me at least) it is more than worth the price of admission simply as that. So for a number of reasons (some possibly unique to me but many, I suspect, not) I really like this book. And I am looking forward to finishing the remaining two-thirds.

- Geof