I have personally known 4 individuals who were trans. Three were M->F (one has since died) and one F->M. All were very nice, interesting, intelligent people. My approach to them was always to let their identity be their choice and to to make NO comment on it and to just respond to them as 'people'.
   Because I can have no concept of what it was like to face the world for many years feeling they had to 'wrong body', I simply strive to see them as THEY wish to be seen, even when facial features give evidence of their original gender. The only thing that I worry about is that I might carelessly address them with their original name and cause embarrassment, so I often consciously avoid names.
Gender reassignment is becoming more common as medical technology advances, and if it results in more human being being comfortable with themselves and each other, it is a positive thing.