Dryer fires are NOT an urban legend. They may be uncommon, but so is any kind of fire. I know I have had the heating element or thermostat malfunction in mine, which caused it to get terribly hot. Another time, something went wonky with the switch and the dryer was still going(and heating) even when the dryer was open.
http://www.usfa.fema.gov/downloads/pdf/tfrs/v7i1.pdf
Here are statistics and recommendations from FEMA on dryer fires. Statistics show that
Clothes dryer fires account for about 15,600 structure fires, 15 deaths, and 400 injuries annually.
The recommendations state:
Never put synthetic materials such as rubber, plastic, foam, or pieces of cloth that have been used to sponge up flammable liquids in the dryer, even if previously washed.
Clean the lint out of the exhaust pipe and the rear of the dryer regularly.
Inspect your lint filter for rips each time you use it. If you see any rips, replace immediately.
The exhaust pipe should be as short as possible and have limited bends to allow for adequate airflow.
The American Household Appliance Manufacturers Association (AHAM) recommends the use of UL- listed rigid aluminum or steel duct or spiral-wound aluminum flex hose, NOT white vinyl hose.
Never let your clothes dryer run while you are out of the house or asleep.
Have gas-powered dryers inspected by a professional annually to ensure that the gas line and connection are intact.