I recently ran across a circular smiley icon with lambertian shading, specular shading, and cast shadows. The effect was a little like a ball on a table.
Here it is:
Clicking the icon toggled an on/off state, from the upper left gray version to the yellow version.
I wonder if the button image itself may be subtly discouraging clicks. In the physical world, a 3d spherical object casting a shadow on a 2d plane isn't something we often push to toggle a reversible state. A push would likely result in rolling it away.
My hypothesis is that a button that looks like sphere on a flat surface would get less interaction than a "floating" sphere in the same position, though I lack an appropriate site to test that hypothesis with.