The iPhone 4S Retina screen is sharp, but one thing I've been disappointed with is the black levels, and this includes the current iPad screens. The black level is very high (i.e. what should be "black" is actually "gray"). This reduces color saturation and contrast and is very noticeable in darkened lighting situations (for example, try reading an iBook in the dark with the "night" theme and turning the screen brightness down). Some of this is backlight leakage around the screen edges and some may just be the nature of the LED technology they're using. Would really love to see closer to true blacks on these screens.
And, it would also be great if you could somehow color calibrate these screens, they tend to ship too blue out of the factory, as most screens do. As iPads are being used for more complex applications, the need for better color criticality is increasing. iPads are increasingly being used for content creation and display. For example, showing clients your photographs or artwork. Obviously you want your work to look as good as possible, something Apple should understand. A lot of people won't need to or want to calibrate their iPad screen, but it would be great for Apple to open a way to do it you you are someone who wants or needs that functionality. Even downloading a separate color calibration app would be fine with me, and Apple doesn't even need to create it, they just need to provide the API for it and storing those settings.
