first of all, ed_the_atom, here is the skript to the above painting. radditzSession.zip
wow your images are terrific. i love in particular the bumpmaterial effect.
now, since this thread gives more and more wonderful information, thanks to michael and ed_the_atom, i transform it herby into an invitation !
though i am a complete newbie at painting i found that it is very fun experimenting with the painting possiblities in zbrush and that you can achieve nice results even as a beginner. 
michael (stonecutter) is helping me to get started with technique, and he suggested the following idea :
let´s paint together, learn and have fun
i invite you all to do paintings in zbrush, any topic, no z-add allowed, but anything else is. post your painting in this thread, maybe with some explanation how you did your image. in this way we will get a wonderful gallery and a lot of information collected in one thread. also if you get stuck with a painting problem, post it here and we all will try to solve it.
i start this “officially” now with this scorpion and will post more images as i make progress or try out new things.
i did first a drawing with southerns zsketcher and you can see the scorpion drawing on the second page of southern´s thread. then i painted first the brown background with low rbg settings so the drawing still shines through, and then the scorpion. i then tried to achieve a shiny look by using the shading enhancer brush.

brush on, have fun and post your results here !