David Hockney and his iPhone.
... Hockney limits his contact with the screen exclusively to the pad of his thumb. "The thing is," Hockney explains, "if you are using your pointer or other fingers, you actually have to be working from your elbow. Only the thumb has the opposable joint which allows you to move over the screen with maximum speed and agility, and the screen is exactly the right size, you can easily reach every corner with your thumb." He goes on to note how people used to worry that computers would one day render us "all thumbs," but it's incredible the dexterity, the expressive range, lodged in "these not-so-simple thumbs of ours."