(define-key gnus-group-mode-map [(meta control g)] 'gnus-group-get-new-nnml)

(defun gnus-group-get-new-nnml ()
  "Get new mail only."
  (interactive)
  (let ((gnus-group-new-mail-list nil)
	(nnml-prepare-save-mail-hook
	 (cons '(lambda ()
		  (setq gnus-group-new-mail-list
			(union gnus-group-new-mail-list
			       (mapcar 'car group-art))))
	       nnml-prepare-save-mail-hook)))
    (nnml-request-scan)
    (let ((gnus-group-marked (mapcar '(lambda (group)
					(concat "nnml:" group))
				     gnus-group-new-mail-list)))
      (gnus-group-get-new-news-this-group))
    (when gnus-goto-next-group-when-activating
      (gnus-group-next-unread-group 1 t))
    (gnus-summary-position-point)
    (gnus-group-list-groups)
    gnus-group-new-mail-list))