Calibrating an iMac is an exercise in frustration. You can't get it dark enough
No longer true with the current iMacs ... easy to get the right luminosity. While not a perfect workstation, iMacs aren't bad, and even the glossy screen is really a non-issue if you are working in an appropriately dim room. Hard to even see any difference if compared to an anti-glare screen in a totally black room.
Under most bright conditions, the glossy screen is actually better, as it is pretty hard to see reflections with normal documents on the screen and the screens are just brighter. I can use my current macbook when riding in a car much easier than my previous ones. As far as bright sunlight, neither works very well, but the matt one can be better if you have some way to use a hood around it.
the main reason I bring this up is the thread title seems to be misstated, the OP was interested in an imac, not a cinema display. thus he is looking at a $1600 investment for an entire computer, quite a bit different than $2500 for a display only. The iMac is functional and printed output can be just fine unless there is some color critical component to it (reproducing artwork, product shots, etc.).
Certainly not the perfect solution, if searching for the best setup, there are much better options.