Mulga:
don't listen to people who are just guessing and obviously don't actually have an imac: the lack of anti-glare coating is a HUGE problem. in my main office where i have a window behind me, this otherwise incredibly beautiful monitor is almost unusable for graphics work. but with the size of this monitor, it is going to be a rare situation where there is not some disturbing interference. lights, windows, or any light colored surface reflect from this monitor's flat surface like a mirror.
unless you are using the monitor in the dark (don't laugh, this is what i do much of the time) you absolutely must have anti-glare coating (try Photodon for quality and reasonable prices) or a hood. if you are doing color critical work, you'll want the hood. (and even then, you need to take care with your workspace with no light source directly behind you.)