Decent book, some good info, but often not well-organized. The biggest flaw is that the authors get lost in the constant silly humor at the expense of content.
Note: This book focuses on the Xcode IDE, and not specifically on Cocoa itself.
Some humor is good, but they spend a bit too much time making jokes and not enough on organizing the guts of what you need to know. If you are really a beginner and haven't read anything else about Xcode then it can be a good starter. The book is definitely informative when it comes to the Xcode toolset—if only there wasn't so much fat to ignore to get at the meat. Many try to skim over the comedy, all the while fearing they may have missed some important fact, since both are intertwined in the writing. To get an idea, check out a sample chapter.