This is really an interesting topic, which bothers me quite a long time until now, this very moment I write this sentence, even though I've been in Germany for three years. It seems that I can never get used to these two forms. Sometimes when I considered I should have been "siezen"-ed, people just "duzen"-ed me, whereas other times when I "duzen"-ed people, they "siezen"-ed me back. Well, it's not anything about grammar, but just kind of feeling, something closely related to respect, I guess. Or again, possibly, I'm too sensitive.
