My parents both bought new Mercury's in 2000, a Mountaineer and a Cougar. They bought extended warranties (100K mile) for both. The cougar needed a new fuel pump at very low mileage, which was covered under the factory warranty, otherwise it had no issues at all. It's currently at 200K miles. The Mountaineer is at 150K, and needed an IAB valve replaced, which was done under the extended warranty for about 160 bucks total cost. We paid a 50 dollar deductable.
My math says about 3 grand outlay in extended warranty coverage, and recouped about 110 bucks of that.