Because of @fred_beecher I setup this iPad Sketch Group on Flickr so we can share our UI sketches. I'm going to slowly post what I work on there.

Freehand design sketching on the iPad is for UX designers. Any app that lets you do freehand user interface sketches, either using finger tips or a capacitive stylus like the Pogo Sketch is what we're sharing here. If you drop non-iPad sketches, they will be booted.

Suggested tools to start: Autodesk Sketchbook Pro, Adobe Ideas, Penultimate, Brushes, OmniGraffle, Sundry Notes.