I love that I can see the callers of a method in Xcode!
"...function is accessed from the Show Related Items menu, or by using the Assistant editor and selecting Callers or Callees in the jump bar pop-up menu..."
So how does one easily popup the Show Related Items menu? Press Control-1 aka ^1 and you will see "Callers(x)" where x = the number of methods calling the method.
There is also the comprehensive Xcode Keyboard Shortcuts and Gestures documentation which covers multi-touch gestures and other shortcuts.
Enjoy this feature while you explore your code!