EDIT: Ubuntu 14.04 sort of supports high resolution screens and allows you to scale the panel and launcher with a simple slider under
System Settings ->
Displays. It's still a bit buggy: it doesn't work for some apps like Spotify doesn't scale and Thunderbird don't scale icons and the content of the emails.
So while Ubuntu took a giant leap forward, the below solution is still the only fully functioning way of scaling everything on Ubuntu.
You can scale everything with
xrandr but the result is not as pretty as it could be if there was true high resolution support.
To scale your resolution, first find the name of your display with
Screen 0: minimum 320 x 200, current 1366 x 768, maximum 1600 x 1600
LVDS connected 1366x768+0+0 (normal left inverted right x axis y axis) 344mm x 194mm
1280x768 60.0 +
1280x720 60.0 +
1024x768 60.0 +
1024x600 60.0 +
800x600 60.0 +
800x480 60.0 +
720x480 60.0 +
640x480 60.0 +
DFP1 disconnected (normal left inverted right x axis y axis)
CRT1 disconnected (normal left inverted right x axis y axis)
So, in my case my laptop display is called LVDS.
Then run the following to scale your resolution:
xrandr --output LVDS --scale 0.75x0.75
The Launcher and Panel might disappear for a moment, but just hover your cursor over them and they should reappear. You might also have to resize any open windows so that they fit the smaller resolution.
I wish there was true high resolution support that was this easy to configure. Sadly even GNOME 3.10 seems to only support changing the font size, even though GNOME handles that a lot better than Unity.