This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
thanks for your question. Especially the first chapters build on one another and you should read them in order. Some of the later chapters (about GCD, Core Data or error handling, for example) can also be read on their own and just expect you to have fundamental Obj-C knowledge that you will have gathered in the first chapters.