My knowledge of microelectronics only stretches far enough to know what to look up on Wikipedia, but that might be enough to help you: http://en.wikipedia.org/wiki/Decoupling_capacitor

Quote:
So logic circuit boards often have a decoupling capacitor between power supply and ground right next to each logic IC. These capacitors decouple every IC from every other IC in terms of supply voltage dips.

AFAIK the actual capacitance value isn't all that critical.

Peter