How to install plug-in in Gimp on OS X?
Solution 1:
You'll find the appropriate folders at /Users/username/Library/Application Support/Gimp/
. There go in the scripts folder
and the presets go in the gimpressionist folder
I found these locations by looking at the GIMP preferences, and clicking on Scripts. The locations cited above were listed there.
Solution 2:
There are OS X instructions in the GIMP documentation and they suggest installing GIMP from fink or macports. Do this and you can follow the Linux/Unix instructions for plugin installation. Otherwise, the documentation states "good luck" if you install it some other way.
However, searching http://gimper.net suggests that, for a Python plugin, you should put it in: [your home]/Library/Applications Support/Gimp/plug-ins
(create directory if necessary).