"Costco only takes their card or MC, no visa. That may have been correct a year ago when Costco's Card was an AMEX. Costco's card is now a Visa, and they accept any Visa card, but not MC."
That is interesting, must vary by Costco. I have not been able to use my regular Visa card at any Costco I have been to, only my Sam's Club MC card. This was within the last month.