In OS 3.1, Apple provides a way to overlay custom controls on the camera view (UIImagePickerController).
However, the properties and methods to do so weren't available in OS 3.0, and as far as I can tell, all you can do is hack the view hierarchy in 3.0.
So, I have a couple of related questions:
1) Is hacking the view hierarchy the only way to customize the view in 3.0?
2) Will Apple reject your app if you hack the view hierarchy?
3) What percentage of people have upgraded to v3.1?
This post provides some insight, but nothing definitive on whether Apple will reject an apps built to 3.0 that hack the view: http://stackoverflow.com/questions/561868/custom-iphone-camera-controls-not-using-uiimagepickercontroller