I think that initially a lot of the 120Hz stuff was mainly Korean ones that had overclocked panels in them or panels that were strobed.  I'd say 60Hz is still the standard for a NON GAMING monitor.  There are some 144Hz IPS panels out now - but the majority of them are still TN.  Once G-Sync and Freesync came out the 144Hz seems to have started being "standard" for gaming rigs - especially with cards that can easily push over 60FPS now.  Some people can't really see or tell the higher refresh as much as the next person but I went from 1080@60 -> 1440@60 -> 1440@144/Gsync and each jump was quite noticeable.  
 
When I was gaming at 60hz my rig could easily push 100+ and I would get some screen tearing and have trouble seeing / focusing on some things.  Enough to the point where I would get headaches after an hour or so of gaming.  Once I got the 144Hz panels all this went away.  The games were noticeably smoother and I could tell that my eyes weren't straining nearly as much.  Now since I have my desktop set to 144hz I can even tell a difference between scrolling web pages between my computer and a 60hz machine.  I really can't tell much difference between 120-144Hz but that's probably because I have gsync.

I haven't personally witnessed playing a game on a monitor with greater than 60hz refresh, so I can't really speak with authority on the subject.
 
When standing still in a game obviously it won't make a difference at all. I think the difference will be when you're moving fast, or turning sharply. In a shooter game if you turn 180 degrees in a half second the view is changing by 6 degrees per frame update at 60hz refresh, which will drop to 3 degrees per frame update on a 120hz monitor, or only 2.5 degrees per frame at 144hz and 2.18 degrees per frame at 165hz. Obviously as a percentage change there's a sharply diminishing return with the higher refresh rates.

I see this on my machine in games that run at 60fps on my 4k monitor. If I turn sharply the image I see gets blurry while I'm turning. I think this reduction in how much the view is changing per frame update during the turn should make this less blurry.
 
Of course this also depends on the monitor's pixel response time, which is the time it takes for a pixel to change from one color to another color. If it can't change colors fast enough, the refresh rate advantage will be negated. 1000ms/144hz = 6.9ms. If the monitor's response time isn't at least lower than 6.9ms then some of the benefit of 144hz will be lost. I think that's right around where good monitors come up, and faster than cheaper monitors.
 
Actually, I just read some really interesting articles while typing this response up. 
 
Factors affecting PC monitor responsiveness.
Motion blur website showing various types of blur and explaining them.
Exploring input lag inside and out.
 
Erma Gerd: check this article out showing measured blur between 60hz and 120hz.

That UFO test on my old monitor was embarrassing. I guess I had gotten used to screen tearing too because once it was gone with my new monitor, it took me awhile to adapt to the awesomeness. I didn't think people had much luck overclocking those 4k Monoprice monitors.... That's cool!

Btw, I looked up how to overclock the monitor, and this Monoprice 4K monitor doesn't cleanly overclock at all. I tried 72hz and it worked fine, but resulted in frame skipping. I used the UFO motion blur test to see this, and the result was that instead of smoothly moving from left to right, the UFOs kind of hitched their way across the screen. I kept going down by 3hz and retesting, and this hitching was seen even at 63 hz. It's possible I might have gotten hitch-free 61 or 62hz, but it wouldn't be worth the bother. 

Oh well, I think we're poised in the next year to start seeing 120hz g-sync displayport 1.3 4K monitors. I'll have to start saving up for one. Once I get another 1080 and go SLI I could actually make good use of such a monitor, or I could do it now on older games that far exceed 60 fps on my single 1080.
 

When Gsync launched and high refresh rates stopped being largely a negative.

sethleigh

agent8
Yeah, that was the one bad thing about those Monoprice monitors, otherwise they are awesome. I got an Ebay Korean monitor and it overclocks to 100Hz without breaking a sweat and it was under $300 bucks for 1440P and zero dead pixels. Kind of a gamble but it worked in my case.

Yeah I did a lot of looking at various monitor options, and was tempted by those Korean 1440p screens, but in the end I decided that 1440p was just a temporary solution since in 2 or 3 years when you can buy a card with the power of a 1080 for $250 I think 4K will become the de facto gaming standard. Of course now I realize the point was moot because my current 60hz 4K monitor is really just a temporary solution until they come out with 120hz g-sync 4K monitors, which looks like this next year. Still, this 60hz 4K monitor will make a great 2nd monitor on the side when I end up purchasing the new higher refresh monitor someday. I gotta tell ya, 4K looks stunning. I'd like to see what the difference is though between 60hz and 120 or 144hz. Now that I've read the articles I linked above I think it's more of a difference than I gave it credit for.

 
Put it this way. I have always owned 60hz monitors. I currently have Dell U2412M, U2415 and monitor in sig. When you move to a 144hz G-Sync monitor. You will be awe struck. And I will never EVER go back to using a 60hz monitor again. Everything is just so smooth now.