The Beginning: A Lucky Break

It all started back in late spring 2006, when I was in the attic, relighting our natural gas hot water heater for the third time that year. By lucky coincidence, the air conditioning blower unit came on right behind me as I sat in front of the water heater. I felt cool air blowing on the back of my neck, right there in the attic. Even as uneducated as I was at that time in the Ways of Efficiency, I knew that this implied a large waste of resources. Leakage in the air system meant that I was expending energy and money trying to cool the attic, which is connected to the outside world. You can't cool the outside world with an air conditioner no matter how much energy you burn. Note for civilians (non engineers): air conditioners do not cool overall, they simply expend energy to move heat from place to place, typically from inside a space to outside it.

Incident: Conditioned air leak detected in attic
Problem: Normal duct aging
Lesson: After 10 years or so, it is expected that air ducts will be leaky in any building, leaking up to 30% of their air conditioning energy in a futile effort to cool the outside world.
Solution: Do it yourself (Google "duct sealing diy" and do some reading) or pay someone to fix it. At the time I paid a local well-known plumbing contractor to perform a full house leakage test. The crew of two men spent an entire day sealing not only the attic ducts, but looking at every airspace penetration (doors, windows, plumbing that goes through the wall) and sealing it. At the end of the day they performed a fascinating test to prove the system was sufficiently airtight (or "tight" in their term): they covered every air register with plastic, and attempted to use a fan to suck air out of the system from the return air vent. The harder the fan worked, the more tight the system. The system was tight. They then sealed off the main house airspace from the duct work, and replaced my front door with a "blower door", which again had a large fan that attempted to blow air out of the (sealed) house. The harder that fan worked, the tighter the seal of the house. The house was tight; the air duct system was tight; the problem was solved.
Moral: Leaky ducts throw away energy and money. Energy efficiency waits for no man! You know what to do.