"Introduced in 1997, the Octopus card was introduced for fare payment on the MTR, but the use of the card quickly expanded for multiple purposes. The card can now be used to pay fares for all public transport in Hong Kong and to make purchases for consumer products at many stores in the city; it is accepted by more than 160 merchants. Some notable businesses that accept Octopus cards include PARKnSHOP, Watsons, 7-Eleven, Starbucks, McDonald's, and Circle K."

http://en.wikipedia.org/wiki/Octopus_card

I hope Oyster Card becomes as widespread, useful and popular. If they keep it as simple as Octopus then it might just work and provide some real benefits to consumers.