I don't know how many of you know about this, but I thought it worthwhile to pass on.
Often, there is a gap between the drywall and the A/C / Heat register. Since this gap is hidden, you have no idea that you are air conditioning (or heating) your attic (or walls).
Most of my ductwork, had a small gap between the edge of the duct, and the drywall. It may not seem like much, but if you do the geometry and measure the area, it adds up. (last months electric bill was under $55)
So....check your registers, grab your caulk, and start fillin those gaps and cracks!