Unless you patch the Cocoa display logic, the fullscreen function won't work for those using Cocoa Emacs. You can still get 90% there using maxframe.el[0].

    ;; psuedo-fullscreen
    (require 'maxframe)
    (setq mf-max-width 1440)
    
    (defun toggle-maxframe ()
      (interactive)
      (if (eq (mf-max-columns (mf-max-display-pixel-width)) (frame-width))
          (restore-frame)
        (maximize-frame)))
    (global-set-key (kbd "<s-return>") 'toggle-maxframe)

[0]: http://github.com/jmjeong/my-dot-emacs/blob/master/maxframe....