Lifetime warranties on products?

I often purchase items with a lifetime warranty. I have never attempted to cash in on one however. Does anyone do this? Must you keep the original receipt along with the packaging for the life time of the product? What does the lifetime really mean? ...as long as you have it? For example I have bought sprinklers with a lifetime warranty and when they no longer work after a few season I throw them away and buy a new one. Can one just pay the postage to send it to the manufacturer to receive a replacement? I bought a flashlight today with a lifetime warranty for workmanship and I'm wondering if anyone has any tips to have this product work for it's lifetime.

Thanks.