I've thought about having the ducts cleaned too. I have dust allergies and I assume some dust is being blown around by the blower through the vents. I guess my evidence is when I pull off a vent and swipe with a white tissue, I get a lot of dirt and dust. I would be curious to know how fast the dust returns once it has been cleaned? I would assume that if there is not filter over the cold air intake, the dust will be sucked right back into the system but then the furnace filter should catch that dust correct?