You caught that quick! It only finished compiling a few minutes ago... (I generally kick off the release builds manually)
EDIT: Looks like emacsforosx does not compile Emacs with support for above command. Will you consider it? I totally understand distributing plain vanilla version though!
But it's frustrating for me, too, because I want the feature as much as anyone else. I've been making do with "(setq ns-auto-hide-menu-bar t)" which is close to the desired behavior, especially when combined with maxframe [1]. It still has the window's title bar, so it's not exactly there.
[1] https://github.com/rmm5t/maxframe.el I use it like this (where super is the command key):
(defun toggle-frame-maximization ()
(interactive)
(if (frame-parameter nil 'mf-maximized) (restore-frame) (maximize-frame)))
(define-key global-map [(super return)] 'toggle-frame-maximization) brew update
# Lion only (or if you don't have xcode?)
brew tap homebrew/dupes
brew install apple-gcc42
# put these in your .bashrc
export HOMEBREW_USE_GCC=1
export HOMEBREW_VERBOSE=1
# /Lion only
brew install emacs --cocoa
brew linkapps