Depends on how you use it. If you pull Apple's trick with retina displays (or an equivalent mode in other OSes) then no, to the user it'll appear the same as a 1920x1080 display, but with crisper text. The point is that pixels are supposed to be invisible, so in the theoretical ideal future, everything would be resolution independent so that decreasing pixel size doesn't make the display unreadable.

It's chicken and egg. The software is set up for bigger pixels, especially on Windows. Higher DPI can mean higher fidelity font rendering in particular. But someone needs to come out with these monitors so that developers can adjust their rendering. MS should possibly even consider pixel-doubling apps, with perhaps some hacks to keep fonts hi-res.

Absolutely.

Still, it has been way too long since there has been any progress in display resolution, so by pushing into "4K" territory it means something like 2560x1440 might just become mainstream.

Win/win: early adopters get the a shiny new 4K display for Christmas, and I get 2560x1440 for less :)

If the applications are designed for the resolution, it would mean a very good PC computing experience where you couldn't discern the pixels at all. I'm pretty excited that this exists, I would even buy one at this price if I was in the states :p.

183 DPI is "too small" for native viewing, but it'll make prettier pictures and more readable text.

I have that very same setup, Dell u2711, and I already find pixels too small. Take hacker news frontpage for instance. Un-freaking-readable.