This is an evolution of a quick processing sketch I did for Golan's class based on a magnetic physics system. I was incredibly disappointed since I built it from scratch without using any physics libraries, but then it just looked like any other pseudo generic flocking blaaaah. So I decided to turn it into an app to generate interesting background patterns for me to use in my illustrations. You can read me talk more about it on the iacd blog.
This video also illustrations the awesome iterative work process you can have in processing, just building off sketches quite painlessly. It doesn't really pay off to work this way in other coding frameworks like Cinder or OF since it takes so long to test and compile, and it really makes more sense to sit down and figure out what you want and then carefully plan and code. Processing kind of lets you just go with whatever whims you have and test them in these quick and lightweight sketches, I love it.
When I have time, I'll paint large watercolor pattern swatches and use them to texture the meshes similar to this sketch below.