I have the X220 tablet IPS screen and it is very clear with good colour reporduction and clarity. Does it compete in anywway with Apple's new Retina in terms of quality?
The Retina display has got to be much, much clearer than the X220 tablet IPS. First, the Retina screen uses many more pixels to construct every bit of detail, and second, the tablet has an extra touch-sensitive layer that distorts the screen somewhat. Puppy
's links show that the Retina screen is slightly brighter and higher-contrast as well.
One thing I have been saying is, get a tablet PC only if you require the touchscreen technology. If you just want IPS, there are other far better choices (Apple's Retina, HP's and Dell's 15.6" business laptops, and several ultrabooks). The fact that you are considering getting a Retina Macbook Pro implies you don't really need a touchscreen.