So here are some paintings I did on some mobile devices, namely the Nintendo DSi and iPhone!
I did this one using "Colors" on the DSi. I think I prefer painting using a DSi and its stylus, plus it is kind of pressure sensitive, allowing thick to thin lines. Although it definitely is not as sensitive as a Cintiq or Wacom tablet. The negatives are the DSi's small screen and the resolution of the final paint isn't that great (512 x 384).Here is a painting of my rabbit Frida I did on the iPhone. I've been fooling around with pretty much every paint program released on the iPhone. I first started out with "Brushes", then moved on to "Layers", since it supported, well, LAYERS. Then I found out about Autodesk Sketchbook Mobile and of the three, I feel it fits my needs pretty well. It supports layers, undo and more importantly, the customization of brushes. Pretty intuitive interface as well.
My main gripe with painting on the iPhone is that it feels too much like finger painting. And it doesn't help that I have big fingers that cover up most of the screen. I've kind of alleviated problem by using the Pogo Stylus. It's small enough to stow away in my wallet, but it has a really spongy tip and I feel that I have to press down pretty hard to make a brush stroke. Another negative against the iPhone is the lack of pressure sensitivity, so sometimes I find myself faking thin to thick brush strokes.
Of the two devices, I'll most likely end up using the iPhone the most since I carry that around with me at all times. I figure that I'll get used to painting on it and maybe bust out something I'm totally happy with. I just found out that they released "Colors" for the iPhone as well, so I'm going to give that a shot and post my thoughts on it later.