i don't mean to sound smug here, really i don't, but not everyone is going to notice a slight color gradient, and not everyone is going to care even if there is one. also, it's sometimes difficult to notice bleed out on black screens if the room is very well lit (IE: The Apple Store).
i'm currently under the impression based on these threads, my own experience and information from an apple tech that 24" iMacs produced before week 20 have issues, and those produced during or after week 20 do not.
my current iMac and my first iMac were both week 10 productions. i'm exchanging it for the 2nd time at the beginning of next week, this time for a post-week-20 production (assuming they have one - they should), and i'll let you know more.
by the way, it's totally great if someone has screen issues and doesn't notice them, or care about them, and therefore select "Only if I did the most ridiculous tests to find out.", but this isn't a "finical" issue for people like myself who run a small home business and rely on a evenly lit screens for imaging and color work... it's not even possible to calibrate these gradient screens with accurate color profiles using colormeters.