Here is a story about not checking your dryer vent.
At a house DW and I lived in about 7 years ago, we never checked the vent. It went from the laundry room across the garage and exited outside.
I started noticing mositure stains on the garage ceiling. Looked like a water leak. Ruined the sheetrock in the garge ceiling. Concerned for the bathroom directly on top of the damaged area, I tore open the ceiling looking for the water source. Turned out that the dryer vent was clogged. Moisture from the clothes we were trying to dry (not all that successsfully btw) was condensing around the pipe and dripping to the ceiling. I had to cut open the dryer vent tube, clean out about a foot of clog and install a new tube.
It was designed so poorly there was no way I could ever clean it out from the inside so I started using a plumbers snake from the outside.
On our current house, the dryer is next to an outside wall so all I have to do is clean out that flex tube every 6 months or so.
Moral of the story: If your clothes don't seem to be drying well, check the vent!