After I upgraded to Leopard, Inkscape did not start up any more. Just a blank screen. Here is what I did to fix it:

If you like Inkscape (an open source alternative to Adobe Illustrator) and have a Mac with Leopard; you will figure that it after installation it will not work. It will say that font caching might take time, but never start. It’s because of a simple bug, with a simple solution. Just open a terminal (Applications/Utilities) and type this, followed by an enter;

mkdir ~/.fontconfig
After that it should start normally.

Thanks to Kuneri for this tip.