My certainteed shingles were installed in 1996 and failed completely by 2008. They were "guaranteed" for 25 years and were included in a class action lawsuit. In the end I had to do stupid human tricks, stand on my head, and produce all kinds of information for them and all they coughed up was a few $100 for a roof that has 45 square of shingles on it
So I listen to the spiel and get sucked into re-roofing with GAF lifetime warranteed shingles. Three years later I'm looking to add a garage addition and I find that GAF has discontinued the shingle (for marketing reasons) and I'm SOL. I ran all they way up the chain to try to locate enough for the project and GAF really didn't give a ****. When I asked what they would do if the product failed during warranty they said they would give me an adjusted amount for the area damages

WTF good is a lifetime warranty if you end up having to re-roof the entire thing when part of it gets damaged or fails.
Around this same time a construction buddy clued me in that essentially there is a dance that goes on between the shingle manufactures and the insurance companies. The shingle manufactures are hoping they can get out of their warranty by blaming it on things like weather or installation as the previous poster said. The insurance companies want to get out of paying for new roofs by blaming the shingle manufactures. In the end, consumers are left in the middle paying huge amount for warranties and insurance and than trying to wrestle a settlement from which ever side backs down first. WHAT A SCAM!!