I pre-ordered iPhone: The Missing Manual and it came in yesterday. The price is a reasonable $13.59 on Amazon. I've read the first 70 pages so far and expect to read it cover to cover in the next couple of days. It's better than I expected.
The pages are well-designed and the paper is decent quality unlike many of the tech books that come out these days. David Pogue liberally sprinkles color screenshots throughout its 292 pages (they are gorgeous because the iPhone screens look so good). I'm guessing that O'Reilly's Pogue Press figure they will sell a lot of these so they could afford to make it a pleasure to use.
Pogue and his team do more than merely regurgitate what is in the free downloadable iPhone User Manual available from the Apple site. You get (1) a more objective description of the iPhone and its capabilities and (2) extra commentary, web links and recommendations.
Pogue makes his case relative to the iPhone's free user manual:
This PDF covers the basics well, but it's largely free of details, hacks, workarounds, tutorials, humor, and any acknowledgement of the iPhone's flaws.
This is a sturdy trade paperback book 5-1/2 by 8-1/2. About a 1/2" thick. I decided to buy it after talking to a colleague who loved the pdf version. I'm glad I did. Unfortunately you can't peruse the book's contents on Amazon. You should be able to find it at your local bookstore, though.
You are promised to receive updated information on the associated Missing Manual website. I tried looking for it and it wasn't there yet.
I printed out the iPhone User Manual pdf. And read about half of it in the first day. This book is more manageable to deal with than a bunch of loose pages or a pdf on the computer screen. And better as I explained above.
I found that although I knew much of the content from daily use, I found reminders of features I had discovered earlier but then quickly forgotten. This is one of the better Missing Manuals that I've read and I've read quite a few.
Since you paid $500 - 600 for the iPhone, it is probably worth your while to spend another $14 to master it even though you can certainly get lots of value without cracking the manual or this book.