It is widely known that lint accumulates over time within the exhaust duct work for the dryer. And that certain conditions can exist that accelerate lint build-up. Generally, the accepted frequency of cleaning is every 18 to 24 months. Proper cleaning involves the use of a spinning brush on a flexible rod and a vacuum or blower for the duct work and some specialty brushes for in and around the actual dryer appliance. Generally the cleaning can take place from either end and in some cases due to length, it is necessary to brush from both ends.
There are several cleaning tools available online and at your local big box hardware store. In my opinion, if you are willing to pull the dryer out away from the wall and disconnect the flex hose from the dryer, the actual cleaning process is not that hard and can save you some money.
In my honest opinion, the LintEater brush system kit (about $29) widely available at hardware stores or online is the best for the do it yourselfer. We actually have them for sale at this link:
http://store.dryerbox.com/LintEater-10-Piece-System_p_58.htmlFor the duct cleaning services there are national franchises and just as reliable, individual sole proprietors right in your community. Consider your Yellow Pages book for Duct Cleaning, Chimney Sweep, or inquire to your favorite HVAC contractor for a reference.
Here are a few national franchises:
Dryer Vent Wizard
Dan's Air Duct Cleaning (CA)
Dryer Vents Plus
Duct911.com
Duct Busters
Ductz
Sears Carpet
This link for a list of cleaners by state:
http://www.lintalert.com/installer_locator.htmTwo good links:
Awesome How-To Video on Dryer Vents and Cleaning By Danny Lipford
http://www.youtube.com/watch?v=eWZx8pC03R8U.S. Fire Administration "Clothes Dryer Fires in Residential Buildings"
http://www.dryerbox.com/news_articles/2007_us_fire_admin.pdf