I just got back and with so many places accepting Octopus it simply made sense. I carried some cash for the "high street" shopping where cash is king, but otherwise I was able to use the card pretty much everywhere. It sure beat carrying around coins and figuring out change.

And maybe this is recent, but the Star Ferry takes Amex now. There were ads for it everywhere at the station. That was the only place I didn't use my Octopus card intentionally, because if you tapped with Amex they only charged 1 HKD ($0.13 USD). It's probably some kind of offer from Amex, not sure if the CC tap function is going to be there "forever" but I'd be surprised if they took it away. They will probably take away that 1 HKD deal at some point though.