I received my 2012 iMac today (3.4GHz i7, 8GB, 3TB Fusion, 2GB 680MX GPU), got it out of the box, fired it up, immediately noticed major display non-uniformity (yellow on the bottom right, blue on the top left, significant brightness variance), and packed it up for a refund. I'm not going through numerous swap-outs again to try to get a good display.
Besides, as I was staring at my new iMac, I realized it's just not enough of an upgrade over my mid-2011 iMac (3.4GHz i7, 16GB RAM, 256GB SSD+2TB HDD, 2GB HD 6970M) to justify the expense. I'll wait to see what the mid-year Haswell update brings, or better yet what the new Mac Pros bring, before I get rid of my 2011 iMac.