I have my retina 15in Macbook pro set to 1680x1050, The setting just to the right of the setting labled best ( retina).
I use 1680x1050 on my 13", if I had a 15" I would switch too 1200p. I really like to get as much space as I can.
1680x1050 for regular use.
2880x1800 for gaming.
I guess I'm the only one who prefers the default 1440x900, pixel-doubled, "retina" resolution. I'm coming from a regular 1440x900 display though, so that's the screen size i'm already used to.
For you guys who run different resolutions, do you notice the performance issues apple warns about? Something having to do with rendering at a higher resolution then scaling down to fit the screen.