I started off buying Beginning iPhone Development from the same publishers, Apress, and that told me I needed to already be familiar with Objective-C. Although I ploughed through it, by the end I realised there were many basic concepts of the language I was missing, and going through all the examples hadn't done much by osmosis to get them into my head. So I bought this book, thinking as it was from the same publisher, it would be the missing part of the jigsaw I needed to understand Obj-C. But no, right up front in this book it says you should have experience with a C-like programming language. WTF? Above the title, the book claims 'Everything you need to know to become an Objective-C guru', when clearly you need to learn another language first, only to un-learn the bits that have changed in Obj-C. And guess what - yes, Apress have the 'Learn C on the Mac' book too (but perhaps that also has a prequel you need to read), and it looks like the one after this before you should start eyeing up that iPhone app you want to write is 'Learn Cocoa on the Mac'. Even with Amazon discount, you're up to £100 before you can even start to look at some of the advanced stuff Apress have planned. I'm beginning to think Apress are the publishing equivalent of the Landmark Forum. There's always one more course you have to take before you can achieve that breakthrough.
Learn Objective-C on the Mac is a good solution if you are coming at it from a C background, but that's not what it says on the tin. If you really want a complete introduction to Objective-C that doesn't assume you've already learnt something else, then a better option is Programming in Objective-C, second edition, by Stephen G. Kochan. A much larger volume, it's true, as it weighs in at 600 pages compared to the Apress book's 337, but it turns out there aren't shortcuts to this.