They ONLY are optimized for 1440x900 on the 15" mbp's !!!
If you try to use the display at 1920x1200 or 1680x1050 ALL the pixels will be BLURRY for pictures, video, anything that the computer does not draw itself.
I'll explain.
Basically the native resolution of the retina display is 2880x1800.
so if you're using 1440x900 then everything is perfect (which is why apple recommends it). Every pixel can be mapped to 2 pixels of the retina display, and everything is sharp.
Many of us know that 1440x900 isn't enough for many types of work (programming, graphics, video editing, web development).
so you want to use the larger resolutions provided (1920x1200 or 1680x1050).
Unfortunately, this means there's no direct relation between the pixels you want to use, and the native screen, so apple interpretes EVERYTHING.
Every single (clear) pixel, gets blurred with it's neighbors, or displaced and doubled, changing the size and shape of the displayed images.
Imagine two grids. One is 2x2 (4 pixels total). The other is 3x3.
Now if you scale up the 2x2 to the 3x3, you'd think you'd be ok, because the 3x3 is bigger, but what do you do with the middle pixel? Which corner's color does it get?
if you choose any color, you distort the image, so the only choice is a blurred mix of all 4 colors. It's a mess.
So a movie can easily look great on a desktop with a native resolution of 1920x1200, but if the macbook has the same resolution (1920x1200) it has to blur all the pixels to match the resolution.
As a photographer all I can say is...
no thanks.
I'm waiting for a 17" macbook pro with a decent native resolution, or it's time for another brand of computer.