Two years after my previous post.
I find the iPhone & the iPad the best platform for mobile art
Brushesapp is awesome.I previously used ONLY Sketchbook pro but Brushes App seemed simple and easy enough to get great art on.
I still prefer Sketchbook for making Vector'ish' graphics
The sucky thing bout brushes app is that it supports only4 layers !.

I still use PhotoFX for rendering some effects ,Its still the No. 1 for photo touchups.

Anyway if someone is seriously considering fingerpainting, For starters it itsnt hard.I recommand you check out Cedric's  tutorials.

Check out this link
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Also Quick note :
My new blog can be found here.Iv turned to micro-blogging.
Cheers '
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*Edit 31-Jul-2011
If you are a mobile artist and use an iPhone/iPad/Nintendo or anything mobile for art join my new group
#MobileArtists