Argh, effing gmail.  resending, to people besides Miles this time (sorry Miles).

On 22/02/2008, Miles Bader <miles.bader@necel.com> wrote:
 > Juri Linkov <juri@jurta.org> writes:
 >  > But even this is not necessary: cua-selection-mode uses C-SPC C-SPC
 >  > to set the mark without activating the region (more precisely the second
 >  > C-SPC cancels the region activation).  This is another reason to enable
 >  > cua-selection-mode by default because this will help people who use
 >  > the mark for navigational purposes.
 >
 >
 > No it's not.  If that feature is desired (seems ok to me), it should
 >  just be added to normal t-m-m.

Well, it does have slight discoverability and ease-of-typing
 advantages over C-SPC C-g.

 Small thing to add to set-mark-command.  Might also be ui-consistent
 to augment momentary mark (transient-mark-mode = lambda) similarly
 i.e.
 when transient-mark-mode is t (perma-on), C-SPC C-SPC deactivates
 mark, but when transient-mark-mode is off, a third C-SPC after
 the C-SPC C-SPC turning on momentary mark cancels the momentary mark?

 Illustrative/trivial patch attached, seems nice in small tests, but
 dunno if there are any awful ramifications.