Nothing is more dissapointing that a flat interface.
A good interface will seem to have dimension, even stick out of the page a bit. The key to providing depth is lighting. The Sphere was created by taking a circular selection, rendering light effects, place a fluffy white spot on the upper left corner, and then a slight drop shadow, and adjusting the color. Light source is very important in creating depth. Add drop shadows to parts that need to stick up from the panel.