Recently I have been using the new GIMP, and I have encountered something rather
troublesome.  The dialog box which comes up when closing an unsaved image
defaults to save.

Now I am aware that this has been reported by another user:
http://bugzilla.gnome.org/show_bug.cgi?id=162837

The response to this was that this isn't a bug, and that all the other programs
are doing it, so the GIMP is going to do it too.  It was then closed as "not a
bug", so I was not able to give my comments.  I'm sorry that I'm starting
another bug report when one has already existed, but I feel I have no choice in
the matter if I want to give my input.

All the other applications may have started switching to "save" as default, but
that does not mean it is the right action to take.  What is most important is
what is best, not what is popular.  I would think the GIMP developers would
advocate this more than anyone else, considering their multi-window method is in
a completely opposite direction of what almost every other art application does:
go with the unified window approach.

So let us discuss: what is best?  Which approach is most beneficial to the user?
 I will put this in a context common to my own experiences (and an experience
which I often see others engage in).  Here I am, working on an art project for a
while.  Let us say I have been saving repeatedy (which I do).  I have been
working for a long time trying to get my picture to look just right, to get this
effect down just correctly.  I've saved my major changes, but I want to try to
make that new modification.  Well, I screwed up. I try and close the window, and
the default button is to save changes.  There goes the original.

Now, you might say, "But if you are accidentally hitting things, you might
accidentally hit the save button in either case."  Not if I am using the
keyboard... it takes significantly greater effort to make that mistake.  The
user should be making a concious decision to press the button to destroy what
may very likely be work they want to keep from before, or keep what they have
now.  The default should be cancel.

This applies likewise to images which have not been saved at all.  In earlier
version of the GIMP, there was not even a "save" button which came up; it
defaulted to discard image, which is just as bad.  It should have been cancel. 
Once again, it should be a concious decision to either discard one's work
entirely, or replace the original copy.  If one is accidentally making an
unconcious decision, and hits cancel, the worst thing that will happen is that
they have to press the x button again.