I noticed something odd today, while using the Mars surface models provided by Jester. The surface models are not obscured by clouds.
Mars' default cloud settings don't seem high enough to cover the two mons. I tried increasing their height signifigantly, up to 320 at the point of the image below, and it became apparent that the .3ds files were not being obscured by clouds as they should be.
Perhaps this isn't normally noticed due to the small size of most surface objects.