This model-view-controller design pattern tutorial explains the role of each of the MVC components, along with how MVC simplifies application development.

The Observer Pattern is the foundation of Model View Controller (MVC) development. In this article, you'll learn how to use it by building a simple email application.

Having separate controller classes for the different sheets seems like a good idea, but can be tricky as well-- basically I just haven't seen enough real world examples of mvc in cocoa to know the ...