If you are a Costco member with a Costco Amex card, and have made purchases assuming you will get Amex’s extended warranty protection, you will lose any such protection when Costco switches to Visa (in 2016).

I called Amex to verify and they confirmed that the extended warranty protection requires being a card holder at the time of a claim (not just at the time of the purchase).

If that coverage is important to you, you might want to arrange to get another Amex card (and of course verify that doing so will provide continuity of benefits).