It's absolutely terrible. I have used 4K and 5K displays in the last year on Windows, OS X, and Linux and the only OS that currently handles these well is OS X.

It's absolutely terrible. I have used 4K and 5K displays in the last year on Windows, OS X, and Linux and the only OS that currently handles these well is OS X. In general, handling high resolution displays requires a really tightly bound ecosystem so scaling works on all applications. Linux makes it immediately clear what happens when this is not the case. 14.04 is totally unusable because you have to either change the system fonts to be huge or scale text within every application individually, if the application even provides the ability to do that at all.