The interactive renderer, used for the viewports, is designed for speed so you can easily manipulate your objects in a shaded environment. It's not the same as the production renderer (see Render Setup Dialog _TOPIC), which is used for your final images. Therefore, a number of effects that are available to the production renderer will not show up in the viewports.
When you design materials, for example, you have four levels of visual feedback. The lowest level is the shaded viewport. The next level is an ActiveShade viewport (or floater). The next level is the sample slot, which uses the production renderer to display the sample sphere. The highest level is the rendered scene, which uses the production renderer to display the scene.