My brother's just written a simple painting program for his TellyMate Shield.
I had a play, and came up with some fine art...
(They're not my hands, by the way - my nails weren't made for photography)
Personally, I think it beats anything done on an iPhone, hands down.
[edit: I forgot to add a link to the 6 button shield that I'm using in the picture above - It's due to be released in the next couple of days]