I've used Python extensively to do (Information) Visualizations, and found the language to be very handy for getting started quickly. I used NumPy a bit, but I mainly offloaded all the heavy display work to OpenGL. I'm surprised that I don't see anything about using Python to develop interactive Visualization techniques, which should be a top priority in 'most' visualizations. (some can do without, but some are built around interaction) Perhaps that would be a good topic for continuing this series =)

Did someone say Quartz? http://www.apple.com/macosx/features/quartzextreme /