I've been mainly using ArtRage to create backgrounds for animation. Because Flash is a vector environment, it can be a bit limiting working primarily in flat colors. I've wanted to experiment with textured and painterly backgrounds for awhile. Above is the opening shot of another short animation I'm working on. The background is all ArtRage; the characters and living room props are all Flash (so they can be animated).
Here is a background I painted for a long panning shot of a destroyed city, burnt to a crisp. Flames were added later in Flash.
One of the short-comings of ArtRage, in my opinion, is that it lacks the ability make a mess or add grimy texture...spray paint, spatters, sponges, drips, etc. I gravitated to tools like this in Painter—or, it was really easy to do in Painter. So, to achieve the effect I had in mind, I created a bunch of smudge and spatter paintings with real—that's right, REAL—watercolors. I made this mess of a painting by dabbing my finger tips on watercolor paper. You can probably make out my finger print in places.
I then superimposed it over a digital painting of the insides of intestines. After some layer compositing in Photoshop, I arrived at the dirty-smudgey look I was going for. I think this might have been one of the first backgrounds I made using the program.
Again, highly recommended! Just play around with ArtRage and see where it takes you!