Google Earth is the greatest thing on the internet next to X and Y and Z, and I love it. However there are some suggestions, not fault finding mind you, but little improvements which would make it easier to use. When something is easier to use it becomes more useful. Some earlier suggestions on this blog were for a fly around tool, a centering tool, and earlier a group of basic viewing control tools. What is suggested here is to put a measurement tool hovering over the various views so it would be easier to judge absolute size of the content being viewed. In the plan view this would only require a measure bar along the bottom of the map which automatically adjusted its size to fit the map being displayed but in the slant views it would require something more sophisticated which would put the measure bars along the side at several specified distances and would individually shown with various lengths.
This simulated 3D map shows a 1 Km arrow and a 10 Km arrow from the left edge of the map to an appropriate place in the map. At other resolutions of the landscape there would be other more appropriate measures placed upon the map from 1 meter arrow when in quite close to 1,000 Km arrow when far away.
It would be valuable to be able to draw a visible path on the 3D map and have its statistics shown. Display such things as distance traveled and altitude changed between the start and finish positions. Perhaps these could also be graphed in a box with the altitude in the vertical and the distance on the horizontal.