Comment 17 for bug 482993

I wrote a workaround for Inkscape.app that does not solve the underlying problem, but at least fixes the symptom: It allows the application to launch and use extensions under 10.6. What it does is to check the system OS version. If it's version 10.6, then it modifies the path-- as used by inkscape only -- to prefer python 2.5. After doing this, extensions work correctly. (I've even been able to write a Mac installer package that applies this patch.)

To use this patch, copy the file (inkscape_10.6_patch) to into /Applications/Inkscape.app/Contents/Resources/bin/

Then, in the terminal:

cd /Applications/Inkscape.app/Contents/Resources/bin/
patch < inkscape_10.6_patch

Again, this is a workaround, not a permanent solution.