[jenniferp]

Perhaps it is a British English thing! Though its not spoken so formally as maybe some people seem to think.
I'm British and if I'm asked "How are you?" I answer, "fine", "I'm fine". I'm living now in Australia and I'm asked constantly when going into shops "How're you going?" and to that I'm answering "i'm good thanks" as "fine" doesnt seem to sound right. I think the trouble is that there are so many variants on greetings and hello's that when you are teaching new learners it's hard to find the one phrase that will be the perfect answer.

I was teaching in a Korean kindergarten and the kids all knew to respond "I'm fine" when asked how they were and it drove me crazy so I tried to encourage them to say other things too, like happy, sad, ok. It started to work after a while - I even had one kid say "I'm strong" but I was away for a couple of weeks and after that it was "I'm fine" again.