One other thing I simply must mention is screen real estate. I have seen a number of posts claiming one of the advantages of the new screens is that one can put more apps on to the screen at the same time i.e. The extra resolution allows for more resizing.
TBH the only time I ever see people doing this is at a computer sales pitch.
I only ever work on the one programme at a time and in the case of MS Word I set that at 150% minimum sometimes 180%. The larger the better, I like the screen to be filled. I do exactly the same when browsing.
What is the point of having a nice screen and not filling it. I work in an office with 60 other people and as far as I see when walking round we all do the same.
Screen real estate is the same as with the non retina iMac when using the best for retina setting (which shows the full benefits of Retina). People that are planning to use higher resolutions and already have an iMac shouldn't consider an upgrade...
The benefits of Retina can be seen only in the best for Retina setting.