I have a stack washer and dryer unit with an indoor dryer vent, and my advice to anyone is to maintain it as well as you can. Invest in a dryer vent brush and cleaner. Keep the indoor dryer vent lint trap clean.
When I first did the dryer vent installation, I ended up positioning the dryer vent hose too close to a wall. The expelled heat had nowhere to go, so that part of the wall got very moist, triggering a mold problem. I got some really good advice from the home improvement store, and I installed a sheet of heat-resistant material on that section of the wall.