Gotten quite a few lenses from HK when they used to have international warranty. Unfortunately now that they only have local warranty, the atrraction to get from there is less. It can be cheaper though and sometimes significantly so. A few years ago i got a Canon EF 24-105L for ~ 1300 when it was selling for 1700 here, and a EF 16-35L II for ~ 1800 when it was selling for 2400 here. So sometimes it's cheaper by more than just the 7% GST we get charged here.
More recently though, I notice the price differential is less sometimes just 10% less. And, the price you get from shop to shop can vary quite a lot. If you find a few decent shops you can always call ahead to check pricing before you go. I usually visit the shops along Stanley Street since it's near my office: Photo Scientific, Chung Pui, Kinefoto. There is a Tin Cheung there too but that's nice to look see since they have nice displays, but not always the best price. Having said that, I got a Lensbaby there.