The Pierre Bergé – Yves Saint Laurent Foundation in Paris is currently displaying an exhibition of David Hockney's iPhone and iPad drawings. The exhibition is on display through Jan 30, 2011.
Hockney uses the Brushes app to create his digital paintings and even has his suits made with a pocket just for the iPad:
He picks up his iPad and slips it into his jacket pocket. All his suits have been made with a deep inside pocket so that he can put a sketchbook in it: now the iPad fits there just as snugly. Even his tux has the pocket, he tells me.