Designing for iPhone 4's Retina Display

So, um, maybe you heard: there's a new iPhone out. For my money (and I shelled out plenty for it), the phone's best feature is the new "Retina display," the eye-popping high-resolution screen. Everything they say about it is true: at 320 ppi, the pixels are just plain invisible. The crisp bright screen really looks as good as print, absolutely gorgeous.

But what soothes the eye also adds headaches for designers. For three years, the iPhone came in just one flavor of screen resolution: the...