Quick Senders and Implementors
Select any selector and do Command-m to see its implementors (Alt-m on a PC or Unix). Select any selector and do Command-n to see its senders (Alt-n on a PC or Unix). It works in any text window.
Browsing Class Hierarchy
In the class list pane of the browser, select a class and choose "spawn hierarchy". A hierarchy browser shows all the superclass and subclasses of a class in the class list pane. Very useful for jumping around and seeing what the class inherits. Try it.
Browsing Inherited Methods
Another great view on code is found in the message list pane. Look at any method, and choose "more..." from the menu (in the message list pane). Then choose "browse method hierarchy", the top item. It brings up a message list window with the current method and all inherited versions. This is especially useful then the method has super in it, or when you can't remember the inheritance chain, or when you want to see how this methods is implemented more generally by a superclass. (In the next release, this item will be called "method hierarchy" and will be on the first message list menu, instead of on its second layer.)
