I've never had a problem returning anything in the 30 days. I don't think you can use your motherboard for skeet practice and expect them to replace it, but any normal damage (blown capacitor, overheating, faulty connectors) they'll replace. After the 30days you have to go through the company (gigabyte, asus, evga, msi, corsair, etc). Their costumer service will replace things too.
I've returned power supplies, motherboards, graphics cards, ram sticks. No problems.