Core77 Show+Tell has put up an awesome video of Converse Design Director, Michael DiTullo, sketching an i-Something in 4-minutes. I always love watching people's drawing or designing process I always learn something new.
"Kids, please try this at home. In this episode, Michael DiTullo and Rocko the Ruler sketch up an iSomething-or-Other in about 5 minutes. Check out how Michael gets multiple tones out of the same marker by varying pressure. Also notice how he starts with the overall form and then overlays layers of detail. The selected perspective is dynamic, but not at the expense of communicating the design. Remember, sketching is a communication tool, and practice makes perfect."