Arrived.
It's very good. Not quite perfect, but certainly very good.
No installation issues - it clearly says to make sure you've installed the drivers before you plug it in, did this and no problems.
Easily runs 2560x1440 on the desktop, and no problems with small embedded videos either. The whole experience is like you're very slightly stressing the CPU and RAM - there's a very subtle feeling of 'this isn't quite as lightning as when you've just reformatted your PC', but it's very, very close.
For video I've had a bit of a play around. There's an 'optimise for video' setting which adds some extra compression, and I've also tried duplicating the main screen (1920*1080) and running some 1080p vids. Is there jerkyness? Yes - probably, if I'm really, really looking for it. On the whole though, no, and once I stopped looking for it it disappeared. I ran a couple of 1080 snowboarding videos from itunes and after 5 minutes stopped looking for issues and started wishing it was winter again.
Running stuff less demanding than 1080p video there doesn't seem to be much point in dropping down res - there's a slight increase in smoothness, but not much.
I can certainly see where the less positive reviews are coming from, but I'd be fairly satisfied.
As it happens though, this is probably all now academic - I've realised that I've been sent the wrong model of zenbook and it's going back! Will most likely take the refund and put it towards something with a displayport.
Anything out there that matches the specs of my Zenbook with a displayport? Was thinking Macbook Pro Retina 15"...