Comment 8 for bug 442642

setting the default unit to 'in' doesn't make a difference here with Inkscape 0.46 and 0.47pre.

Could you start Inkscape from the command line to see if you get any error messages?
Keep X11 running, but quit Inkscape. Open 'Terminal.app' and type:
   /Applications/Inkscape.app/Contents/MacOS/Inkscape
(replace /Applications with the path to your installed Inkscape application)

any console messages should now be printed in the terminal window. (To kill the program if it doesn't respond to 'Quit' anymore you can use 'ctrl+c'.)