Most people already know that World Wind's elevation data is far better than what Google Earth uses. What most people don't know is that you can use your own elevation data as well, it is just not that easy to do.

As you can see in this post on the World Wind forum:

... using more or less the same method than for the images
Our company developped its own set of tools to process the DTM and integrate it in WW.

On this page you can see some examples of GE terrain data, World Wind terrain data and the user added terrain data.

Here is an example of a location in GE:

GE Terrain

Here is the same site in WW:

WW Default Terrain

And with user processed high resolution terrain:

WW High Resolution Terrain