From the same 'meetthegimp' thread as the previous poster, patdavid, but my version is sufficiently different to merit a post of its own, I think.
Should work in Linux and Windows and have a few more options so had to rework the dialog to barely fit on my Windows portable!
If place in '~/.gimp-2.x/plug-ins' and for Linux make it executable; it appears on the Image menubar at 'Extensions/Plugins-Python/File/Info from Exiftool...' after (re)starting GIMP.
If you don't like that and don't know how to change the menu placement, consult "http://registry.gimp.org/node/27031#comment-15104".
Those plug-ins date back a couple of years and they are not for the novice user; it explains why not published here before.
Don't forget that exiftool works on a file not the image in GIMP.