Hello,
My name is Olga. I live in Sitges, and there is a name for girl that is very commom: Vinyet. My family name is not very commom. There is a web that you can write your family name and you can see how many people in Spain has the same that you. The page is INE Distribución territorial de apellidos. I think is very interesting.
When I meet somebody usually I use his surname except when is a friend that introduce me, then normally I use his first name.
We don't use surnames without the title Mr. o Mrs. We only do it when there are two friends with the same name, sometimes you do it in a kind way to call them.