Man, I got the best (early)birthday gift this year in the form of the ipad touch. And I knew that I had to buy sketchbook pro. So far I'm loving it, though the pogo stylus that I separately purchased is pretty poopy. You're better off with your finger until they make some better for artists.
Regardless, this sketch was done in sketchbook pro on the ipad and then taken into PS for some clean ups and corrections as you can see from the two images above. It's awesome that you can actually export your sketchbook files as a PSD. and email it to yourself. Very nice!