I got to thinking about the amount of effort involved in the construction of one of these blasted capacitors, which may fail badly, causing you great discouragement and irritation along the way. Here I have attempted to suggest things which could be done with even a "useless" GC, so that it can still produce some good science.
One of the things which you might think of first is the usage of your cap in a Tesla coil. I feel that this has very good possibilities, however, Tesla science and resonant harmonics can be another daunting problem to look at, especially if you are already feeling down from a non-working GC.
This will depend very much on your dielectric. If your GC can get up to around 25 kilovolts without exploding or setting itself alight, then this may be for you. If you already have a Brown gravitator or electrokinetic apparatus, then the mass of charge stored in the GC could be put to good use. Put a large resistor in series with the GC to stop the wire from bursting, and to ensure a steadier, slower discharge. Close the circuit, and bleed the GC into a gravitator. The effect will only be visible for a short time, but you will accrue larger amounts of charge on your gravitator than before, and will subsequently experience greater thrust from the device. In this way, the GC has still indirectly created an electrograv effect, and it will be useful in further experiments.
What about a rail/coil gun? Heh - discharge it quick and dirty through a step-down coil and one of Bill Beaty's Hi-amp hoop-coils, and you will get a brief pulse of supercurrent. Over two thousand amps or more are theoretically possible if the capacitor was completely and rapidly discharged. Useful for all those interested in electroballistics.
If you have any crazy suggestions, please feel free to email me at EclipseG@Angelfire.com