Vizio just released their new 4K tv's. Like Scott R
posted a few days ago, I also hit Costco yesterday and picked one up moments after it came off the truck.
I won't be using this as a TV. This is the new PC monitor.
(edit #2)
After fighting with the Vizio P for a month to get it to do 4K@60hz, I've returned the set and replaced it with a Panasonic AX800. 4K/60 right out of the box, with full 4:4:4 chroma support, unlike the Vizio. See below... The Panasonic is 10x what the Vizio was.
Let. Me. Tell. You.
Iracing @4K is FREAKING INSANE! 
Even better on the Panasonic. Nice, smooth motion, no 30hz judder/skipping with fast motion.
Next up is a new graphics card with HDMI 2.0 to support the 4K @ 60hz.
EDIT
Ok, it's been about two weeks since I got this set, and I wanted to give an update.
While it's still "Glorious" I am quite disappointed with it, overall. Here's why...
HDMI 2.0 is needed to pass 4k resolution at a 60hz refresh rate. With the introduction on Nvidia's new 900 series cards, they're the first cards to feature HDMI 2.0. You would
think that 4K@60hz would be a no-brainer, right?
Wrong.
Vizio neglected to include 4:4:4 chroma (basically, full-color) support @4k/60, possibly due to a limitation of HDCP 2.2 inclusion. Then, Nvidia neglected to support 4:2:2 chroma support over HDMI. Leaving the user with what might be a 4:2:0 or 4:1:1.
This means that 4k@60hz does not work. 30hz is laggy, and unusable for
smooth gaming. Mouse skipping galore. As long as nothing is moving, it looks freaking stellar.
I can set to a 2650x1600 resolution @30hz. As with the 4k, looks great... until you ramp it to 60hz via a forced custom resolution, then it looks like crap, as with 1080 below...
1080p resolution at 60hz looks good, even better than the previous Vizio I was using as a monitor. But ramp it up to 120hz, and all text becomes a blurry, crayon-like mess due to down-sampling of chroma. About 75% of color information is tossed out.
Chroma subsampling - Wikipedia, the free encyclopedia
Here's an image showing the difference...
Basically, that's it in a nutshell.