I tend to use Emacs for all my editing, although when I am writing Mac OS/X GUIs, I couple it with XCode for managing the project build process. The main things I've needed to customize in my ".emacs" file is to get Emacs to automatically recognise Objective-C files when they are opened (including Objective-C ".h" files), and have the "compile" command in Emacs call xcodebuild to actually compile the program.
To have Emacs recognise Objective-C files, first add the following to your ".emacs" so that ".m" and ".mm" files get handled automatically:
(cons '("\\\\.m$" . objc-mode) auto-mode-alist))
(cons '("\\\\.mm$" . objc-mode) auto-mode-alist))
Next add this code
so that header files get automatically handled.
Finally you can compile using xcodebuild with the following code:
(defun bh-compile ()
(let ((df (directory-files "."))
(while (and df (not has-proj-file))
(let ((fn (car df)))
(if (> (length fn) 10)
(if (string-equal (substring fn -10) ".xcodeproj")
(setq has-proj-file t)
(setq df (cdr df))
(compile "xcodebuild -configuration Debug")