Mine froze shut, or at least small enough that the dryer stopped drying two winters ago. Luckily it was near the end of the season so I just used the laundromat a few times then it warmed up and thawed.
Then I procrastinated getting it cleaned and the same thing happened last winter. This time, I bought some extra venting tube and a plastic box that you plug one side in to your dryer and the other side in to the wall vent, and it has a switch and a screen that lets you pick between venting inside or outside. Heat and humidity are in demand during the winter, so it was a win/win. My clothes came out dryer and faster than ever, plus the heat and humidity were appreciated.
I got the duct cleaned this year.