USB3 port
Thunderbolt port
Fusion drive
USB3 is not really a huge concern for me because my USB devices (apart from my multi-card reader for my DSLR) would not benefit from speed and downloading photos to my computer is plenty fast for me with USB2.
Fusion drive is great for someone that wants better IO performance coupled with large storage but I would be set with a 240GB SSD since I use a NAS for large file storage.
I would like the latest and greatest but I am still deciding if losing the optical drive and better video card (while paying $100 more) is a worth-while investment for me. I should also mention that the SD card slot has been re-located on the back which makes it a lot more inconvenient to access especially if you frequently need to do so. It kind of forces you to use an external card reader which will permanently take up that USB port.
Another thing that concerns me about the refreshed model is the modding capabilities. By that I mean changing/adding HDDs, upgrading CPU etc. The mid-2011 iMac is pretty easy to mod but we don't yet have any details on the late 2012 models.
Anyways, I ordered a 27" refurb. which should be here on Thursday. I will see how I make do with it and wait for the new 27" to be released before I make my decision. In the meantime I would love to hear your comments/experiences/suggestions.
One major reason I see for going with the late-2012 is the laminated glass to the screen. Based on the amounts of posts on various forums about the iMac screens, it seems to be a big issue with dust getting into the LCD panel assembly after some time, requiring an LCD replacement. While this may not be fixed in the new model since the majority of users report dust inside the LCD and not in between the front element and LCD screen, it may be worth noting.