Final gathering tips and tricks
The following steps are designed to help you eliminate noise and optimize scenes that require final gathering:
To avoid noise and other artifacts especially while rendering sequences, don't add too much color to the material of the objects you want to use as lights, increase their size instead.
In 2.0+ you have an auto compute button which evaluates the correct settings for FG according to the size of the scene. Once you modify the scene don't forget to recompute.
Don't keep the global ambiance (modify>ambiance) setting to 0, instead add a small amount, it will increase the bouncing of colors and better illuminate the scene.
You may try to use several different colored cards (3d objects with a bright constant material) for light sources instead of just one this will encourage the light bouncing effect and give more complexity to the scene.
If you require realistic reflections you may want to look into HDRI images as environment maps. Basically an hdri image contains a lot more information than a regular bitmap image. Therefore, the result on reflective surfaces will be more precise. Info on High Dynamic Range Images could be found at Ed Harriss' site at http://www.edharriss.com/tutorials/tutorial_xsi_hdrinxsi_english/hdrinxsi_eng.html
HDR sources can be found at www.debevec.org/Probes/