I just installed Gimp 2 for windows along with the latest GTK+ runtime and noticed that it exhibited the same font problem I've been experiencing for ages with matplotlib. I was getting WARNING **: Couldn't load font "MS Sans Serif 8" falling back to "Sans 8" errors. It's addressed in their FAQ, <http://www2.arnes.si/~sopjsimo/gimp/faq.html>, reproduced here:
# I installed Gimp 2.0 on Windows 9x/ME or NT 4, and I'm getting a lot of messages saying ** (gimp-2.0.exe:4294830849): WARNING **: Couldn't load font "MS Sans Serif 8" falling back to "Sans 8". What should I do?
# You have two options:
* Go to Control Panel->Display properties->Apperance tab, and set all fonts to Tahoma (or any other TrueType font).
* Uninstall GTK+ 2.2.4, then re-install it without the GTK-Wimp component.
I took option B and now all is well with both Gimp and Matplotlib.
I'm running Win98 and the Gimp FAQ entry hints that it may be a problem in Win98,ME and NT installations. It might be worth adding this to the Matplotlib faq page next to the "On windows with GTK, I'm getting lots of messages about not finding the Times font" entry.