Should be cleaned regularly. We use a local guy in town that makes that his business - Stuart at LintFree Dryer Vent Cleaning, LLC. $99 and he takes care of everything in about 1/2 hour. The cleaning before last he found my wife's drivers license in the vent. It went missing and she had gotten a replacement. Amazing to think that made it through the dryer's blower and everything.
Pretty amazing to see how fast clothes dry after that vent is cleaned.