WSJ writes about the spreading tentacles and increasing success of Octopus:
the payment method, known as the Octopus card, has done more than just replace pocket change on the bus. It has become a widely accepted electronic currency, used to buy a newspaper at 7-Eleven, a meal at a fast-food restaurant, even coffee at Starbucks.
In all, more than 12,000 locations across Hong Kong accept the card, including parking meters, municipal swimming pools and the popular horse-racing tracks.
About 1% to 2% of all cash transactions in the city are made with the card, says Octopus Card Ltd.
Octopus is a stored-value card and behaves like a debit card. Money is subtracted when the card is held over a reading device, which is a low-range radio transmitter that can be incorporated into doors, turnstiles and countertops. Because reading devices can detect a card through leather and plastic, many people never remove their card but rather wave their purse or wallet over the reader.