When the Retina MacBook Pro was announced, I was excited that one of my favourite hardware features from iOS had made its way onto the desktop, but as a designer I was wondering what the best methods would be to design for it. I was also eager to take advantage of the extra pixels and make our apps look even more stunning! I quickly managed to work out a way that felt comfortable designing Retina apps for the Mac, and one that could also crossover to iPhone and iPad app design.
A lot of this applies to the iPhone/iPad too. Worth a read.