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With the last 10.8.3 update the text even at 1920 x 1200 (15" rMBP, of course) becomes noticeably smoother and crisper at the same time. It was fuzzier prior to the update. I'm running mine @ 1920 exclusively. I've never even considered 1440 x 900 because as I did with my old MBP, I find at that scaling the desktop is pretty much unusable (for what I do).

1440x900 is great for normal use because it's everything well-sized and your eyes do not have to suicide.

1680x1050 is great while working on Premiere Pro.
 
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