We are too lazy to change the tyres depending on season or the type of riding we are doing, so our tandem has had 700x35 Marathon Pluses on it every since it was built. In 3.5 years we have done 15,000 miles, quite a lot on audax rides, but also some cycle camping tours with a heavy load. In that time we have had two punctures - although we have gone through a couple of pairs of tyres in that time, so some tyres must have gone life expired without ever getting punctured.
No doubt they have been a bit slow, but we aren't planning to change any time soon.