Word of warning: not one of the 5-star reviewers actually worked through examples in this book then reviewed it.
It's not a 5-star book. It's a 5-star topic, and sadly (very very sadly) it's the only book I know of actually on that topic.
I think the author's intentions are good, and there's a lot of useful info. I'm grateful to have it.
But all of that has to be balanced against the maddening b.s. of trying to actually follow his examples. You know, to actually do what you're supposed to do with a programming book.
Up to chapter 5, it's a pretty good book. If you download the code from the publisher's web site, you'll discover that he names some of his objects differently than you would if you follow his instructions strictly. This actually will create problems for you potentially when you try and troubleshoot problems in your own code, but they're minor. Annoying and needless, but minor.
Then you get to chapter 5, and it's really not so minor anymore. Grab the book (print version or PDF) and work through the examples in chapter 5, and you will have a broken program. Don't take my word for it. Check out the forums and the errata page on their website, and you'll see others reporting the same problem. There is a complicated data migration described. After walking us through a fairly trivial example, he then goes on to give us a much more complicated version. He leaves large portions of that to the reader, and just goes instead for code. The problem is that he doesn't even give us some of the most important code. He shows us a very important ObjC method to add to the AppDelegate... but never even mentions the major alterations you need to make in another method to make that new one get called.
Perhaps it's unreasonable to expect programming book editors to actually go through the examples to see if it works. Perhaps it's unreasonable to expect all books to be as well-done as Hillegass' book.
What's sad is that I've been waiting for this kind of book ever since Core Data came out. And there are some very nice ideas here. I'm gonna slog through the rest and hope it gets better, because the topic is really important. If you plan to buy this book and really work through the examples, I think I'd still recommend it (since there's nothing else). But word to the wise: it's gonna require a LOT more work than a properly written and edited programming book would have.