Just had a great idea. No idea how feasible it is, if Apple will allow it, or if it will have to be for a jail broke iPhone or iTouch.
It would be cool have an IDE app for the iPhone/iTouch. It could support WiFi and Bluetooth for communicating to the Arduino. If possible a modified dock cable could be used to connect via USB to the arduino. Of course generating sketches on the iPhone/iTouch will be tedious but think of the ways you could use it.
I'm pretty sure Apple would reject it since they keep such a tight hold on there hardware. I doubt they will allow the dock to be used in that way. But i'm sure someone here has some experience in the iPhone SDK and would know if it doable or not.