Lyndsay Williams of Girton Labs has built this prototype "SenseSurface" system which allows you to attach real, physical knobs to a flat-panel display. The magnetic knobs are measured by a sensor plate in the rear, letting you turn the knob itself to control the software dials. It's all a test project now, but I could see some people really getting into this. (Although not on laptops so much as dedicated displays.)
Below, a short clip of a prototype SenseSurface knob in action.