Just a quick note today. I’ve previously written here (and also here: whoops!) about my UIButton+NavButton category, which I use to create my own “back” buttons for navigation controllers, so that I can cross-fade them properly.
It turns out that the code (header here, implementation here) works just fine on high-resolution devices. The only thing you need do to completely support such devices is to provide some high-resolution artwork. Just grab the high-def email@example.com and firstname.lastname@example.org images and include them in your project; the runtime will detect and use them automatically when appropriate. (Leave the original artwork in place for standard resolution screens.)