I'm only up to chapter 4, but as there are no reviews on Amazon thought I'd at least post initial thoughts. So far I am quite liking the book. The first couple of Chapters have a good overview of the tools you use to create iPhone apps, and I'll take the publishers' word for it that the chatty, quirky style aids in remembering things. However, I've completed Chapter 3 and whereas previously, everything was explained, this chapter starts picking apart Objective C and makes constant comparisons to aspects of the C programming language without properly explaining them. I'm sure a lot of people who want to start programming for the iPhone will be unfamiliar with C, and likewise will be a little confused by cursory references to "malloc", "alloc", "mutexes" and so on.
I'm going to keep at it, and will post more when I've got a bit further. I'm still optimistic I'll be creating my own apps by the end!