If Quicksilver is running you must have a ~/Library/Application Support/Quicksilver/ folder. There is common confusion if you don't know that ~/ stands for you home folder. Don't confuse it with the system Library folder, note the difference between:
Thanks! I knew about that, but I had forgotten it when I started troubleshooting (and Spotlight doesn't search these places, so I found no folders named "Quicksilver"). Apparently it also needs to be a scripting file, one of a few types.
In case anyone in this group uses Mathematica, here's what I was doing: http://programming.garron.us/quicksilver/mathematica.htm
A hack, of course, but much simpler than trying to write my own MathLink through Applescript or Objective-C.
-Lucas
