Visit some of the links below for some great resources:

American Lung Association
Should You Have the Air Ducts in Your Home Cleaned?
IAR Publications
US EPA
National Air Duct Cleaners Association (NADCA)
North American Insulation Manufacturers Association (NAIMA)

Dryer Vent Cleaning Links:

Consumer Product Safety Commission - Overheated Clothes Dryers Can Cause Fires
Dateline  -  Using Dryers safely 
WHNT News 19 Live - Could Your Dryer Catch on Fire? Mine did
Dryer related fires
Underwriters Laboratories Inc. – Product Safety Tips