By default, the front dial controls aperture, the rear shutter speed in Manual mode - and you get an old fashioned needle display for under/over exposure. It's fantastic!
In Aperture priority, the front dial controls aperture.
In P and Auto, clicking the rear dial in lets you scroll through white balance, ISO, AutoBracket and exposure compensation settings.
These parameters can then be changed really quick by then using the up/down controls on the 4-way control pad. It's intuitive and way, way faster than, say, the V3.
I got the 21mm lens today and it's a beaut. I'd wager that as soon as you get this camera in your hands, you'll want to go out and buy one. It's a real photographer's camera!