I've done the trip to Hong Kong. Yup, it's long.
If you have a good sleeping pill, take it. My husband (who hates any and all air travel) has to fly to Europe a lot for work. He takes a pill at the start of the flight, and it puts him right out.
You've done transpacific flights before, so you probably already know this, but it bears repeating. Get up and stretch and walk around the cabin during the flight. If you sit still for the entire flight, you run the risk of DVT. So, once an hour or so, take a little walk.
Have fun in HK, it's an awesome city.
