This could be added as a new option to the user preferences, so that
some options could be saved accross sessions.  This could be done in
the same way as the gfig-path, gflare-path and other plug-in options
are saved in the gimprc.  AFAIK the current gimprc API for plug-ins
only supports strings, but it should not be a problem to convert the
integer to/from a string when it is saved or loaded.

But there is a problem with the user interface: this setting should
probably not be saved to the gimprc every time the user changes it.
So where should be the dialog that can set the default?  Should it be
in the JPEG plug-in or in the Gimp itself, along with the other user
preferences?  From a code point of view, it would be better to leave
this to the JPEG plug-in, since it would be the only one dealing with
this setting.  But from a user interface point of view, it would be
better to have all persistent settings in the Preferences dialog,
which is controlled by the Gimp.

*** This bug has been marked as a duplicate of 63610 ***

For information, a part of this problem has now been solved:

2003-08-05  Raphael Quinet  <quinet@gamers.org>

        * plug-ins/common/jpeg.c (DEFAULT_QUALITY): increase the default
        quality setting from 0.75 to 0.85, as requested in bug #61088 and
        in bug #63610.  This seems to be a more reasonable default for
        most users.  The correct way to solve this problem would be to
        implement the persistent preferences as described in bug #63610,
        but this quick fix should take care of the most annoying problem.