I changed my name by deed poll to DPs surname. I use the title Ms. We all wanted the same surname, just as a symbol that we are a family unit, we did give serious consideration to using my original surname or even a completely new name, but in the end we thought we might as well take the easier route and go with DPs name. When I changed my name, I actually saw it as more changing to have the same name as DD than DP.
Keeping my own name wouldn't have exactly been feminist - all I would have been saying, in effect, was that I still belonged to my Dad, rather than my DP.
We did consider things like my mothers original surname, but again, that is just my Grandad's name really.
I always put DDs name as Miss, as she is 2 and definitely a child, but I will encourage her to start using Ms when she feels she would like to be considered as an adult (I'm thinking around the age of 16 or 18, but it is her choice)
What is far more annoying is this tendency by some of my friends to insist they are "girls" and not women. These are sexually active adults who have jobs and houses and, in some cases, children. To me, a girl doesn't generally have these things. It seems creepy to me.