Sketching interfaces is a path focussed on generating many ideas and finding the right design. Lately I've been thinking about how to adapt the activity of physically sketching on paper to get the same results in Mockups. On the Balsamiq UX blog, I wrote about a technique I've been experimenting with to do sketchboards in Mockups using a Symbols library.

http://blogs.balsamiq.com/ux/2011/04/28/sketching-in-mockups/