I've had my younger pit bull mix insured through PetPlan for 4 years. For the first 3 years, we had no claims, and the insurance rates increased at a reasonable 10%/year as he aged. This past year, we had a porcupine encounter and then a serious car accident which ended up costing over $4800. PetPlan reimbursed us without a fuss; each time it took about a month for all the processing. I don't yet know if they'll increase our rates dramatically after 2 accidents, but my guess is that they'll continue on the regular rate increase schedule of 10%/year.
I hate to think of the tough decisions we might have had to make if we didn't have insurance. Our dog ended up healing better than the vet thought he might, so we didn't have to put him through some of the very expensive reconstruction surgeries that we initially thought would have been necessary. Those would have been difficult to approve without the insurance. Even though the odds say that pet insurance usually isn't worth the cost, when something really expensive happens, it's good to know you can make a decision based on what's best medically, not what you can afford.