Absolutely agree about keeping an MC and a Visa backup. While 95+% of my monthly volume is with merchants that take Amex, I sometimes find myself using the MC/Visas to complete specific promos as well as at the rare place that doesn't take Amex. There have been enough "3 stays with a Visa" or "Buy your AA ticket with an MC" bonuses recently that it's worthwhile to have the cards in your wallet.

As for EAP, if the whole exchange scheme breaks down (which it inevitably will), you still have effectively a 1% rebate card. It's not like you will totally be left holding the bag. I know we like our miles better than we like money to spend on eBay, but it's better than nothing.