I just finished the book « Sketching User Experience » by Bill Buxton. This book in my view is an important book. It will have a profound impact on the designer community. They will say:
“WOW, I should have used this or that sketching technique and I would have saved huge amounts of time and money instead of building those expensive prototypes”.
It broadens the concept of sketching to the user interaction or in other words user experience.
The objective of a sketch is to verify an idea rapidly and cheaply. Bill extends the concept to user experience. He describes a multitude of sketching techniques such as Wizard of Oz, Video, and paper mockup as a way to test user experience rapidly and cheaply.