I just bought the 70 inch from Costco in Orem, UT. Looks like they had 4 of em on the shelf. Now they have 2.
First one I brought home had a cracked panel, tested the second in store and all was well.
i went for the square trade plan, $80 bucks for it. They said the price had just changed from 100.
As far as the TV is concerned, mostly very happy. Obviously I don't have many devices that support it, but got netflix streaming at 4k and it looks quite impressive. For non 4k content, the upscaling seems to do a pretty good job. Netflix super HD of the avengers looked great especially considering netflix compression. My TV (Google Fiber) looked decent, but I only really tried more compressed networks (FOOD, HGTV, etc), will try ESPN and networks tomorrow. My non-HDMI 2.0 onkyo receiver has 4k upscaling (only to 30 fps obviously) so I am going to compare it to the built in upscaler before deciding on my final configuration.
Default color options are way overblown (vivid mode), but the "calibrated" option (at least to me) had very accurate colors and looked fantastic. The black levels are really impressive for an LCD. The backlit and active zones seem to work well.
I have one minor annoyance so far, when CEC is on, audio from the built in apps (at least netflix, haven't tried others) doesn't get output to my reciever, with or without an optical audio cable. I have to turn off CEC and use the audio cable. But it does seem to be passing 5.1 (need to double check).
The UI is good and surprisingly snappy. Remote is nice, especially with the keyboard on the back (much better than the slider model they used to have).
All in all, I am pretty happy so far and think that its probably the first viable 4k TV for general consumers. $2500 for a 70 inch backlit LED is a pretty good deal, even without it being 4k. Now I just need a video card for my HTPC with hdmi 2.0