Nice book among other books I ever purchased for iPhone development. It's simple and easy to read. Can be used as a reference to most of the iPhone essential functionalities without going through alot of unwanted talk like what other books do. It uses articles-like chapters for each feature so you are not forced to read it in sequence. Great. Keep up the simple job :)

finally a guide that's not for the previous generation Xcode, but for Xcode 4