I find that the xcode-builtin-documentation reader is hard to use. I want to see the root of all Guides available, to get an idea of how long I will have to keep reading until I can start. All the time some new Guide pops up to me, and I am wondering how many they are.
Is there an overview somewhere?
The whole documentation can be browsed online on developer.apple.com.
Leopard Reference
http://developer.apple.com/reference/
Leopard Guides
http://developer.apple.com/documentation/
Almost always the search gives quite accurate results, so use either google
NSString site:developer.apple.com
or use the search field on the page.
Additionally one should say, that if you right click on an article in the Xcode help, it offers you to open the document in the browser.
Start with http://developer.apple.com/mac - there are lots of docs there.
For Cocoa, your starting point is Getting started with Cocoa. For Objective-C, your starting point is Object-Oriented Programming with Objective-C. In each of these documents you will find links to other documents.
The root of Mac OS X API is Reference Library. From this point you have access to all other documents.