I've had the monitor for a week so thought I'd share my thoughts:-
Out of the box the front bezel (The one with the Predator logo) is not flush to the monitor in one section, you don't notice this in day to day use unless you look down from directly above the bezel, build quality is otherwise fine.
The panel's a good one in terms of picture, minimal BLB, no dead or stuck pixels, a really nice display, excellent image.
Unfortunately mine won't "over clock" to 100 Hz it will only do 90

(95 flickers occasionally) It's clear that ACER have pushed the hardware really hard to achieve the OC. What's unclear is whether or not Acer consider not being able to hit 100 Hz a fault; there are mixed messages around the forums apparently quoting Acer on this matter.
However when running at 90 Hz the overall quality of the display, gsync etc is excellent. I've checked for the scan lines issue and on my display and if your face is two inches away from the screen on the left hand side you can notice the slightest hint of it, but honestly from a normal viewing distance it is not an issue for me.
The LED lights underneath the front Bezel are a really great touch, it does look the biz!
I have seen the WFS issue on a couple of occasions but this only seems to happen for me when the LCD lights are switched on in the OSD during sleep.
If you put all of the above together ... well.. if your in the market for a new monitor I'd wait, £1K's a lot to drop on a display that has a number of issues. It is however much more of a difficult decision (re returns) for those of us that have already purchased it because once the monitor lands on your desk, what it gets right it does really well.
My personal inclination is not to return the display but to wait for Acer to sort out the issues re WFS etc and then consider a return under warranty. (You pays your money you makes your choice.. right!?)
The biggest issue for me is the lack of support in a number of games for the 3440 x 1440 screen size, this was unexpected on my part and I wish I'd paid it more attention prior to purchase.
Another reason for those of you in the market to perhaps hold off purchasing a 34 inch display for a few months until both software and hardware issues are addressed.