Many people are tempted by the low cost of Apple products in Hong Kong compared to all other countries around the world, including USA. They are most attracted to the factory SIM-unlocked iPhones sold through official Apple resellers and Apple HK store online. So they are tempted to purchase one or more of these products while they are travelling to Hong Kong. Making a purchasing decision like this should not be taken lightly. Aside from the cost, for any electronic product there should also be consideration of warrantee.
Fortunately, Apple had changed its warrantee last year for all its "portable" devices (ie. MacBook, iPod, iPhone, iPad, etc.) such that they have a worldwide warrantee coverage. But you need to read the (not so) small print in Apple's warrantee documents. Apple has the rights to request any warrantee services to be performed in the purchased country. Of course, this is less likely if the country where the warrantee requester is in also officially sells the item in question.
In some cases, people who lives in Hong Kong may want to consider purchasing Apple products from other countries. One such example, is the current situation with the iPad, where they were sold out within one day and Apple Premier Resellers have stopped receiving pre-orders because they can no longer promise a date on which to fulfill the backorders. Fortunately, for people who lives in HK, by this Friday (July 30th) Apple HK will be officially selling every Apple released products. Therefore, the chances of Apple HK requesting purchasers to send the warranted item back to purchasing country for warrantee repairs is low. So if you have the means to purchase iPad or iPhone 4 from UK or France, and willing to pay the higher cost due to exchange rates, you can.
Please understand I am not suggesting you purchase from the gray-market sellers in Mong Kok or Wanchai. These resellers are charging approximately HKD1000.00 above List price for iPads and close to 200% more for the iPhone 4 (from UK or France), lower for the ones from USA.