My last project was a bunch of Python scripts to geo- and time-tag scans of analog photos. As interfacing with other OS-X programs was not the most enjoyable part of it, I have written down a bunch of the tricks I've found. For example, they allow your Python programs to query Preview for the currently open file, to ask Google Earth for the geographical coordinates at the center of its screen. See the whole thing at Python and Applescript in OS-X.