in normal use, the screen bleed doesn't affect me that much, only when i'm working on dark images / night shots in full screen (which can be often), but the color shifts are constant and most annoying... my screen is calibrated in those shots too, it's much much worse with the default iMac calibration.
i can't be without a computer for any period of time really, so i have to wait until i go on vacation to send it in for fixing. the apple store isn't close to me so i didn't really have the option of going there repeatedly - i live in the city so don't have (need) a car, and renting a car to go to the apple store to hopefully get an iMac with a good screen isn't something i was willing to do continuously... once was bad enough.
when it's time for me to send it in, if they tell me they won't fix it i'll freak out at them.
I'm going to return mine today for the exact same gradient issue that you have. Going to wait a couple of weeks and then buy one again. Reading that dantay got a good display brings me hope that I'll be able to eventually.
Also, I've heard that there is a 30-day replacement or return period for DOA merchandise with Apple. You could argue that your computer is DOA, as I definitely don't want to have to settle with that gradient for a $2000 computer.