I went to one 28" 4K monitor. Just as many pixels as before, all compressed into a higher PPI...it is beautiful. I can't wait for 5K. Not having a second monitor is annoying for real estate management reasons, but Windows 10 (and OS X.next) will support tiling on the desktop, so no prob in the long term.

I have have a notebook with internal hybrid graphics and the max number of external monitors connected. Whenever the configuration changes the utilities installed along the actual drivers (Intel and Nvidia) begin to fight for who gets to configure the layout. Monitors go on/off seemingly randomly for a few seconds. As I only use the multi monitor setup when the machine is docked, I don't care about that funny dance every morning. But there's an administrator profile on this windows machine that reproducibly locks up when in multi monitor mode.

When I was using 2-3 monitors, I had all kinds of trouble with them under linux. This was no doubt mostly due to them being different orientations, but there were no end of driver/window manager issues with various distros. Windows always worked flawlessly.