In this season of shopping, it’s worth knowing that stores are not allowed to require a minimum purchase for use of a credit card. They are also not allowed to require that you present photo ID to use the card. Consumerist has the scoop, including where to report violations.
This isn’t just a US law, it’s a condition set by Visa, MasterCard and American Express. I know that it applies in the UK, and probably most other western nations.