It may not be one of the most exciting things to do (kinda like having your car worked on), but performing regular maintenance on your dryer venting system is essential for safety and also extends the life of your dryer. Consider this, a dryer vent is only four inches wide and even with 1/2″ of buildup around the inside of the vent, your dryer vent is now only flowing through a three inch opening.
As the dryer vent becomes more and more restricted, it causes the dryer to work overtime and the additional buildup of lint can easily cause a dryer fire. The danger can be even greater if you are using gas dryer, you now add in the extra hazards of carbon monoxide and potential gas leaks.
In summary, always be proactive about dryer maintenance and always make sure a professional is servicing your system such as a CSIA certified dryer exhaust technician.