Creating /etc/gimp/2.0/fonts.conf and adding
<fontconfig> <match target="font"> <edit name="rgba" mode="assign"> <const>none</const> </edit> </match> </fontconfig>
fixes the problem.
This is the solution I went for.
It turns off subpixel rendering for GIMP, and it isn't a such bad idea as it sounds like at first, due to the fact that GIMP uses it's own subpixel-rendering anyway.
This is a better solution than the one in post #4, since that solution affects all programs, and not just GIMP.
<fontconfig>
<match target="font">
<edit name="rgba" mode="assign">
<const>none</const>
</edit>
</match>
</fontconfig>
fixes the problem.
]]>http://www.waersekuj.nl/images/branding-new-1.xcf
Edit: couldn't get the image tag to work
]]>Why does my anti-aliased text look like that with the horrible green boarders?
EDIT: Solution is in post #4. Works great now: