GIMP Version: 2.7.4
Operating System: Windows
OS Version: XP - SP3
GIMP Experience: Beginner Level

List any relevant plug-ins or scripts:
the majority of http://registry.gimp.org/

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In version 2.7.4 Regular GIMP for XP 32 bit (http://www.partha.com/) everything -most importantly for me: that GMIC, Mathmap, all filters and plugins python (after a small addition to the libraries - tcl; pygtk), apng and PostScript (pdf, ps, eps) of gs902w32.exe. - works perfectly (except eyedropper - troublesome error foreclosure menu File and Edit -repeated on different computers !).
The Portable version is bad (I have tried many) - how Python - does not work Mathmap - and vice versa (never all).
If, for anyone in XP (32 bit) all of these programs work - please comment and give source download ....

PC has a version of MathMap that works in Gimp-2.7 versions MareroQ.
I have Parthas Gimp-2.7.4 installed and it runs perfectly with everything.
GAP
MathMap
GMIC
PSPI
Python

MathMap, Gap , python , PSPI and many of other plugin works all well in my Portable (from Partha Gimp 2.7.4)

Only problem add preference path break portability...

If you wish you may upload my copy, has MM, Gmic, GAP .FF converter . ACE. Gimpscripter, as collection of animation and artistic and "path" scripts and plugin, read/open for PDF, EPS, Flash (swf) and WebIP files,...and much other list is too long
i also removed texturizer and sharpfeather (that give a error at start up ) and the apng plugin

BUT my copy will work only if your main HD is "C" and if you place directly in C ( As i wrote before add prefrence paths in preferences break portability , so will work only from the same position )

Thanks PhotoComix, thanks Rod !
Just because I'm curious why?
Gimp Portable placed on any hard drive is working properly (with the appropriate settings in the Preferences) - after installation on USB keys have (main HD is "C" also preferences is a with a well) already unfortunately there are problems - example Mathmap.
Probably not the point - this may depend on a Pendrive and type USB ?

http://www.gimpchat.com/viewtopic.php?f=4&t=1789&p=34198#p34198

if you want add preference plug-in paths
use edit GimpLauncher.cfg text file instead of preferences menu
for example
if you want to add new plug-in path at settings/plug-ins1 and settings/plug-ins2
add this line to GimpLauncher.cfg
plug-in-path|settings/plug-ins1|settings/plug-ins2|1