Well, I went a little crazy with Ceterumnet's iPhone case, thing #22572. The images are roughly in the order they were created. This is absolutly inspired by RichRap, who was the first that I saw do live filament swaps. Most of the credit should go to Alexrj at slic3r. org for All the cool patterns in Slic3r.
I modded the Greg's Wade's Adrian's extruder so that I can switch filament on the fly. I basically made the hole below the hobbed bolt into a funnel, so that the Cut-N-Follow filament switch would work. I did this with a single extruder, 3mm filament and a 0.46mm hottip. I also uploaded my modded Greg's with a Budaschnozzle mount because Thingiverse requires a model to publish.
I only print in PLA because ABS is bad for the planet. It's also pretty.
If you use this technique, please upload your images as a derivative. I can't wait to see where people go with this.