Re: air ducts / dryer vent cleaning
I read a Consumer Reports article on having your air ducts cleaned--the conclusion was that it's pretty much a sham. 1.) You really don't need to clean out the dust in your air ducts. In fact, 99% of the dust in the air ducts stays in the air ducts because it is magnetically attracted to the metal in the ductwork. Cleaning your air ducts will likely agitate the dust and make the problem worse. 2.) The only "bad" thing in your air ducts is mold, and if you have mold in your air ducts, then you have a bigger problem--probably a leaky A/C or a leak in your house. Cleaning your ductwork does not address the root cause of the problem.
A nice HEPA air filter or five will most likely address any indoor air quality issues you might have.
The dryer vents, on the other hand, are definitely important to clean regularly. RedsBaron's story explains why.