When I first got my iPad I bought it for the sole purpose of using it as a sketchbook for my ideas. I know its no photoshop, but there are some big advantages. You can do some amazing designs with the effects apps. Forge of neon is one of the best. It makes an animation into a 3D object. Every design is different as is every viewpoint and you can change the colours.
Here are a few of my favourite experiments
