So far I haven't had any issues with it. Gaming wise, I love it, it's the best screen I've ever used, but I've never owned an IPS. The build quality is excellent. It feels *VERY* sturdy compared to my old VG248QE, and the rotation mechanism feels a lot less... Flimsy isn't the right word, but it's what I'm going to use here. The 24" rotated pretty easily, sometimes to a fault. The PG278Q takes a conscious effort to turn it, you won't be accidentally tilting your screen every time you reach over to change the OSD.
Bringing that up, the OSD is a joy to maneuver and very intuitive. Took me all of seconds to figure out. No "gotchas" that I've noticed yet, I haven't tested ULMB yet. 1080p@144 Hz works just fine too, for anyone who might need to step it down a notch. GSYNC is everything it's cracked up to be, but I already knew that from my modded VG248. I have yet to try 3D on the monitor, but I imagine it will be impressive.
I will say, you can't enable ULMB on the fly. If you're already in a game, you can't use the Turbo switch to go to 120hz and turn on ULMB. You have to turn off GSync first.
The only thing wonky (like I mentioned the need to do it before) is the color calibration out of the box. It's a touch warm for my taste, and a touch dim. But the OSD lets you adjust that, as well as the Nvidia control panel. Also, the monitor does put out a decent amount of heat, and its a bit warm to the touch while you're using the OSD buttons, but nothing that I would say needs to be concerned about.