*** Bug 51561 has been marked as a duplicate of this bug. ***

This is blocking the use of other programs like Nautilus or GQView to
open images inside gimp (You can only open one). I think that the
priority should be reconsidered.

OK, I have set the priority to "high", acknowledging the fact that
other applications cannot use the Gimp correctly until this feature
is added.  However, the feature will only be added when someone takes
the time to write the code and submit a patch.  Changing the priority
does not ensure that the feature is added sooner...

Note that there are several ways to implement that feature.  I do not
think that the "single instance mode" should be the default, so using
a separate client program similar to gnome-moz-remote (as you
suggested) or using command-line arguments as described in bug #51561
should be considered when implementing this.

By the way, there is already a "gimp-remote" program included with
gimp-1.2.1.  I think that it should be sufficient for Nautilus and
other programs.  The way it works is not perfect (it relies on DND
and it does not work well if you have hidden to toolbox using Tab)
but it should work for simple operations.

What is missing from "gimp-remote" that blocks its use in Nautilus
or GQView?

Great!, I already emailed GQView's author to suggest him the use of
the gimp-remote command and I am fileing a bug in nautilus right now.

Perhaps this bug should be resolved as wontfix and another bug be
filed for the problems you described using gimp-remote.

Just for curiosity, what is the use of having multiple instances of
the gimp? From Raphael's comments I deduce that there is some use for
it, I thought it was just waste of memory and desktop space...

Thanks!

From John Ellis (GQView's author):

Newer version of GQview already use 'gimp-remote -n' as default to run
gimp, you
probably have the older default of 'gimp' as the command if you:

a) are using a rather old version of GQview, and/or you

b) have been using GQview for a long time (see below)

Upgrading will not adjust to the new command automatically. In any
version of
GQview, edit the 'gimp' editor slot in the preferences dialog - change
"gimp" to
"gimp-remote -n".

Hope this helps,
John

I opened a bug on eazel's bugzilla about nautilus not using
gimp-remote: http://bugzilla.eazel.com/show_bug.cgi?id=7968

OK, I set this to "WONTFIX", according to your suggestion.
The problems with gimp-remote are now mentioned in the new bug #52866.

Regarding the reasons why one might want to run multiple instances of
the gimp on the same display, here are some things from my own
experience:
- At work, I have access to many machines and I frequently run the
  gimp remotely from another host.  Sometimes I copy and paste some
  images between a local and a remote instance of the gimp.
- While debugging a script or developing the gimp itself, it can be
  very useful to run different versions at the same time (for example
  the stable version together with the current development version)
  and to compare what happens in both versions.
- If I read a bug report that describes a way to crash the gimp, it
  is useful to be able to test that on a second instance, instead of
  crashing the one in which I am editing some images.

Thanks for the answers! Now, something else, while trying to move
everybody at work from gimp to gimp-remote I had some complications.

I've noticed that gimp-remote is not included on Ximian's RPMs.
(however, it's manual is there)

Is that a problem of The Gimp or Ximian's?.

If its Ximian's, how/where can I report the it?

The missing gimp-remote command is a problem in Ximian's distribution.
This command is part of the standard Gimp 1.2.x package and should
have been included in the RPM.

I have reported this problem to Ximian:
  http://bugzilla.ximian.com/show_bug.cgi?id=2120