Beware pickpockets, especially in places like ChungKing Mansions or other well populated locations such as the Ladies Market or Temple Street market. I managed to have a wallet lifted there, and was not aware of it until I returned to my hotel. Fortunately, it was my 'daily' wallet that had only a small amount of cash and no credit cards in it.
I have to say that these guys really are masters of their 'art'.
You have been warned and no, it is not a problem specific to Hong Kong