Leaking HVAC duct system causes a bunch of problems

I recently had some major problems with the duct system in my house.  Because of this, I ended up doing a great deal of research and learning a lot about ductwork.  The duct system is actually an air distribution system.  It is a branching collection of pipes that distribute the heated or cooled air from the HVAC system to different rooms.  This network of pipes not only supplies heated or cooled air, but returns the same amount of air back to the HVAC equipment in a continuous cycle.  My duct system was leaking, and by the increase in my energy bills, I figured it was losing about thirty percent of the heated or cooled air provided by the HVAC system.  This was making the HVAC equipment work a lot harder, and my house was no longer comfortable.  The duct system in my house is located in the walls, ceilings, attic, basement and crawl spaces. The heated and cooled air was escaping into these spaces, instead of warming or cooling my home. It was also sucking outside air into my home, introducing pollutants, fumes, and humidity.  I was suddenly dealing with problems with indoor air quality, unpleasant odors, and health hazards.  I inspected the duct system and found leaks around the joints where the pipes are connected, around the air handler unit, and near the vents.  There were small holes and the mastic had eroded along the joints.  Sealing the duct system is beyond my capability, and so I contacted a local HVAC contractor to handle the job.  The HVAC technician first performed an energy audit and confirmed what I already knew.  He told me that my duct were leaking a tremendous amount of energy.