Zilch! I'm too new to knives to give you any first hand insight, but I think that generally warranties on any product (short of defective out of the box) are pretty meaningless.
I'm in the Building Materials Business and recommend that consumers purchase a product they like, especially if aesthetics are involved, like roofing, bricks, windows, etc as the manufacturers leave themselves too many opt outs to make the warranty have much value.
My guess, with knives, as with most products, stick with the reputable manufacturers and forget about the warranty.