I like reading the first few words of lifetime warranties.  They usually say something like, "This product is guaranteed to last for the entire life of the product."  Wikipedia clarifies:  "This is not to say that the product is guaranteed for the lifetime of the consumer ... A lifetime warranty is a guarantee on the lifetime of the product."  So in other words, a lifetime warranty says a product will last as long as it lasts.  After it dies or ceases to work, it'll no longer last.  Ah, lawyers.