GIMP 2.6.8p1 OSX PPC 10.5.8
GIMP strangely copies some or all of the .app directory to a new directory called /tmp/skl. This directory is owned by the user running GIMP, and it is NOT deleted after the user quits GIMP. As a result, no other user on the system can run GIMP, because other users can't access the skl directory created by the first user that runs GIMP. The problem may be because the developers never operate on a multi-user Mac, or because their multi-user setup uses promiscuous permission settings that allow other users to access the directory /tmp/skl.
Suggestions: delete /tmp/skl when quitting GIMP,
OR delete /tmp/skl when starting GIMP,
OR create /tmp/skl and all its contents with the proper permission settings (suggest POSIX permission settings, since they are much simpler and more portable than Apple's ACLs)