Hopefully this should answer some of your questions:
http://forums.creativecow.net/thread/8/1161034
Bottom line - both the current OS and the Retina MBP are fine with 7.0.3 - the only issue I'm having is the 'change resolution' bug where FCP needs you to turn on and off external video monitoring when you change resolutions - which you will do with the Retina. In addition, the HDMI output doesn't seem to give smooth playback when used for video monitoring in desktop preview mode of external video settings.
The weirdest thing about the retina display is how it looks pin sharp at any resolution - I use FCP7 mostly in the 'more space' mode which apes the 1920x1200 display on my old 17" MBP, and it looks great.
I love the retina - the size makes a difference when travelling, and the twin thunderbolt and HDMI outputs make extending to other screens and fast storage very easy. Oh- and the 512Gb of FLASH storage is stupidly fast (I could actually recommend occasionally editing off it - and viewing broadcast masters) and makes the high price tag actually look somewhat reasonable.
Ben
Edit Out Ltd
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FCP Editor/Trainer/System Consultant
EVS/VT Supervisor for live broadcast
RED camera transfer/post
Independent Director/Producer
http://www.blackmagic-design.com/community/communitydetails/?UserStoryId=87...