gistfile1.el

;; open the current (file's) directory in Terminal.app
(defun mac-open-terminal ()
  (interactive)
  (let ((dir ""))
    (cond
     ((and (local-variable-p 'dired-directory) dired-directory)
      (setq dir dired-directory))
     ((stringp (buffer-file-name))
      (setq dir (file-name-directory (buffer-file-name))))
     )
    (do-applescript
     (format "
 tell app \"Terminal\"
   do script with command \"cd %s\" in window 1
   activate
 end tell" dir))
    ))