Good news for Unity users with HD displays. Unity now supports UI scaling. In simpler terms it means you can scale all the Unity Desktop UI elements to an extent comfortable to you. Usage of infinitely scalable SVG icons further facilitates it. The goal is to support HiDPI screens better where the UI elements look tiny otherwise. The feature is still under development at the time of writing (introduced recently and on Trusty Beta) and has issues. For example, when I reduced it to a value less than 1 for a crispier desktop, the fonts in Dash search became distorted. But when it is ready, it will be an absolute delight for screens with 2000+ resolution like Retina displays.
To tinker around with it search for Displays in Dash and you will find a slider towards the bottom of the display settings window. You can also set it using gsettings:
$ gsettings set org.gnome.desktop.interface scaling-factor n $ gsettings set org.gnome.desktop.interface text-scaling-factor n
where n is the scaling factor. A value of 1 means default and 0 means autodetect.