Like a prior reviewer, I'm using this primarily as a PC monitor, though I've also used the Netflix app. I'm also running it at 4K/60/4:4:4 via HDMI; no settings adjustments were required to attain this through the TV itself, but only Nvidia Control Panel (by default, it runs at 4K/30/4:2:2, I believe). So far, it's been absolutely perfect, in this function. No dead or stuck pixels (at least that I've noticed), no visual or input lag that I've noticed, and no backlight issues (bleeding, spots, etc.) that I've noticed. Color, brightness, etc. are all perfect, basically out-of-the-box (though I did increase backlight to maximum), and very few adjustments are required to make this look pristine. The stand is functional, but, of course, it isn't adjustable like a monitor's (aftermarket VESA desk mounts are available--this is my next step). Also, there's no "auto-detect" as with a monitor, so you'll need to manually power it up and down each time you use it (small price to pay for such real estate at such a low price, in my opinion). The only issue I've encountered while gaming at 4K is that a handful of older games (I've tested around a hundred, so far) seem to want to run at 24 Hz, if at 3840 * 2160; if you encounter this issue, simply create a custom resolution of 3838 * 2159 @ 60 Hz, then disable scaling (to keep it pixel-perfect); they'll then run at 60 fps, assuming that you have the hardware (I'm using two GTX 970s, which are surprisingly powerful enough for most of my collection at 4K/60/maxed [some with additional SSAA, etc.]). (Let me tell you this: there is absolutely no going back to 1080p gaming after seeing this, my friends.)

Else, the included Netflix app indeed supports Ultra HD (costs $2 more/month, and content is extremely limited, but you're future-proofed) (haven't tested the others apps yet). Contrary to another reviewer, there is indeed an internet browser (I'll attach a picture as evidence.)
Basically, what you're getting here are four 20" 1080p panels (without bezels in between them), so as you might imagine, as productivity goes, it's incredibly helpful (e.g. four full-size 1080p browser windows open at once). I've not tested other 4K televisions as monitors, but this one, so far, is flawless. Seating distance note: the proper seating distance for a 40" 4K is 2'11", give or take, for someone with 20/20 vision; coincidentally, that's precisely mine, and as expected, it's just the point where pixelation becomes slightly visible if I move any closer. (So, at my seating distance, 40" is perfect.) If you're considering a 28" 4K monitor (which go for around $300, at cheapest [unless Korean]), rethink that decision and give this a chance--you won't regret it. Any questions, feel free to ask--I'll do my best to respond. Recommendation: buy it, and buy it while it's $329!
p.s. you won't need a "special" HDMI cable. Any halfway modern HDMI cable will support 4K/60/4:4:4.