Now that Emacs has moved to git, maybe it's time to start contributing directly? Here's how you build Emacs from source on OS X:

git clone git://git.savannah.gnu.org/emacs.git
cd emacs
./autogen.sh
./configure --with-ns
make install
cd nextstep
open Emacs.app 

For more info and instructions for other distros, see Lars' post.