After being thoroughly disappointed with Erica Sadun's contribution to the iPhone development book scene I stumbled on this gem.
The writing style is fantastic, and the way it is put together works very well for teaching - at each stage you learn things and they seem to stick. The way it progresses and builds on the knowledge you have works very well, and I really enjoyed all the tips and tricks the dropped in for Xcode and Interface builder - I've been using these tools for traditional OS X development for a few years now and still learned a lot.
About the only thing I could ask for from this book is 'more' - just keep going instead of ending :)