I created an action that does this automatically, using a series of paths, channeling, setting masks, etc. First I created a brush-over of the subjects, then used it as a subject mask while applying a sequence of sketching paths. It's about a 400-step Photoshop process. I used Komix font from Dafont as well. I tend to stay away from the filter gallery for the most part, by the way.
Here is another effect (without the speech bubbles) that I use as well with a bit more saturation. I don't link this to the full-sized image, though.
