A basic principle in engineering is that in order to extract energy from any source, there must be an energy gradient. For instance, you can have oodles of electrons at a certain point, but they won't supply energy, unless there's another point with fewer electrons you can connect to, and cause a current to flow. For every energy "source," there must be a corresponding "sink," in order to get at the energy. If this "zero point energy" is EVERYWHERE, where is the sink?