Ok another easy but important change is:

Limit the zoom-out level. As of now it's easy to crash the app with one too many clicks on the "-" button. (and losing a drawing to a crash is frustrating!)

(edit) I think this is the app that completely transforms the device for me. I'm starting to see the potential here for a real killer app.

Edit: A collection of hi-res vintage b/w photos (sfw) to use for sketching motifs. http://www.shorpy.com/