The short of this one is that you plus your DSLR camera (Canon currently, Nikon in development) into your computer), run a server on your computer, and then run DSLR Remote on your iPhone and -- Boom! -- you can get the live preview right from the camera lens on your iPhone, adjust all sorts of settings like white balance, ISO, etc. and "fire" pictures off when you've got it set up, and set on, just exactly what you want.
The long of this is, with iPhone 3.0 coming and it's APIs for peripheral connection via dock and Bluetooth, we ain't seen nothing yet. It's not hard to imagine more and more gadgets (and even appliances) suddenly taking advantage of what could be one of the most flexible and powerful "remote controls" on the market.
If iPhone 1.0 was multi-touch and the interface, 2.0 was App Store, 3.0 is still looking to be all about the accessories.