I speak Cantonese when I was on holidays in HK with my boyfriend. My boyfirend doesn't speak Cantonese, but he knows a few basics. So in my duration in HK, I would be talking in Chinese and then in English. I realised that I sometimes end up answering my boyfriend in Cantonese! It was so amusing for my relatives (red-faced for me) when they noticed what just happened. It's great that many people accepts me and boyfriend. Even the security gaurd in the appartment block said "Good morning!" to my boyfriend, but my boyfriend would just answer "Joh sun!". He would say the same to my relatives, and gave them a surprise. Locals would definately respect you more when you speak Chinese. But I am lucky that it is obvious that I am from abroad, but would all speak to me in Cantonese in shops etc... It was great! From my experience that has been really enjoyable in HK for both me and my boyfriend.