Hi Michael,
Are you changing the vertical position of the shader (Y coord) and expecting to see changes? The shape shader doesn't really work like that. It applies its displacement to the surface independent of its Y position. The displacement is added to the surface, so the displacement is relative to the surface rather than the shader. If you set the displacement amplitude to 1000 the surface will always be displaced by 1000 regardless of where the shader is positioned vertically.
A side effect of this behaviour is that you can't use the shader in displacement mode to make an area perfectly flat, at least not using only the shape shader. Say you have a hill in the middle of the of the area covered by the shader. If you set the displacement amplitude to 1000 it will move that hill 1000m higher, not make a flat surface at 1000m.
I'll look into making some changes to the shape shader so the displacement can optionally be relative to the shader and therefore dependent on the Y position.
Regards,
Jo