I have a Dell XPS13 developers edition laptop with Ubuntu 12.04. I am connecting the laptop to a Dell U2413 monitor via a minidisplay port on the laptop. I am able to connect the two and mirror my laptop on the monitor, but the laptop is unable to detect it as a display (i.e I cannot use it as a dual monitor setup). Also, when connected it tend to flicker on and off.
The native resolution of my laptop's 15.6" display is 3840 x 2160. Unfortunately, I found that the graphics on many applications didn't scale appropriately for this resolution, and were pixelated/blurry despite checking or unchecking the option in the Compatibility pane for "Display display scaling on high DPI settings".