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.
The other issue is the compiling of the sketch to a hex file. It was discussed a bit back with 'normal' bluetooth phones and a java app but I think the issues with writing the code and compiling made it stop there...
So would that prevent an app being made that could receive data from the arduino. It would be great to use with the arduino in the field to gather sensor readings and whatnot.
You can already communicate with the arduino via the iphone/ipod touch's serial (if the device is jailbroken). There is a page somewhere but I dunno where it is.
Then you would just need an app for receiving and saving serial data (I think there is a non arduino related one somewhere). Presumably you could also use the arduino bluetooth for data transfer with an app to pair up and receive serial data that way.