Two days in HK, and I think DCC is kind of omnipresent here.

However, they are all very clear and easy to opt out (the ones I've encountered). Usually, the cashiers (today at 翠华 in 铜锣湾 and yesterday at Hong Kong Station MTR) would opt out for me, and I actually receive two slips at once, with one showing confirmed HKD amount. Just now at Tom Lee Causeway Bay, they asked for my currency preference after seeing the choices on the terminal. Hitting "cancel" means HKD.

My guess would be that rogue DCC terminals are always in Bars here in HK? Regular shops and restaurants seem fine.

One negative thing is that with US cards that don't have PINs, the terminals will be in the cashiers' hands when DCC appears, so some inexperienced cashiers might bring problems.

I bet with ubiquitous signing pads like the ones in the US, or PIN pads like the ones in Europe/Australia/NZ, the choices would appear right in front of the customers, which reduces the chance of wrong input.