I personally think Hong Kong is one of the few countries in the world that has embrace and rolled out one of the most pervasive wireless payment method in the world, where you practically get to pay parking charges (see above image I took with my Nikon D90), supermarkets, taxi, 7-elevens etc. all with the Octopus RFID card system.
While some other countries are struggling to stem down mishandling of revenue from parking charges for example, HK seems to have done such a great work in integrating many core infrastructure services with the ease of payment from these wonder. Well, its not a ground-breaking technology but the execution for mass adoption is well commended for the city.
I remembered running short of cash one day with my kid in the subway, clamering for a drink out of a sudden. The availability of paying a cake shop via Octopus saved my sanity within a few minutes! Wow! Cool!