[makecheck]

If you feel comfortable with C++ to some degree, this transitional document might be helpful: http://ktd.club.fr/programmation/fichiers/cpp-objc-en.pdf

I've found it does a good job of explaining how Objective-C works, for someone with C++ background.

As far as interface design, I feel that Cocoa is something you just have to tinker with in order to learn. Apple has lots of sample code (register a developer login on developer.apple.com if you haven't). While there's plenty to read, I feel that to really understand things like connections and controllers in Interface Builder, you have to try to build things or inspect the interfaces in sample projects.