I was recently in Hong Kong for a holiday and used my Visa for 9 transactions (most of them card-present ones) and saw that 8 transactions that has posted are in HKD.

At one of the merchants (Admiralty MTR to purchase Disneyland and Oceanpark tickets), I had a bit of a scare when the sales clerk passed me a slip to indicate HKD/SGD and I ticked HKD. While the final slip given to me indicated I was charged in HKD, it was an offline transaction, and I received a sms notification from my bank that I was charged in SGD (about SGD2 more after accounting for the foreign transaction fee on my card). Subsequently I was relieved that the charge posted in HKD.

At another restaurant in IFC, my friend was presented with the credit card machine, and asked to press the green button to be charged in SGD and red for HKD. Very counter-intuitive, but at least the restaurant and machines were DCC-compliant. For the other transactions, the sales clerks generally charged HKD without asking.