We had a VW Passat in the shop this week on which it appears the client forgot to replace the timing belt at the recommended interval. The car is in perfect condition otherwise and all of the other maintenance items had been taken care of. The original belt went over 190,000 miles, well beyond its recommended life, before it broke.
When the belt broke it left the customer stranded on the highway at night, but worse than that, it did significant damage to an otherwise perfectly good engine. We had to remove the cylinder head to have all the bent valves replaced along with the normal items you would replace with a timing belt. The long and short of it is what would have been a several-hundred-dollar maintenance service turned into a several-thousand-dollar engine repair.
If your car has a timing belt, check the mileage against the recommended service interval for your car and be sure to perform this service on time. Not doing sot can be very inconvenient, not to mention expensive!