Strangely to Anglo-Saxon eyes and ears, it is normal in Spain for a Sr. (Mr) Sanchez to sleep with Sra. (Mrs.) Perez. It's not because they aren't married. In this still slightly macho society, one thing that feminists might like is that women do not change their surname when they get married. Indeed, people don't just have one surname, they have two. The first is the father's surname, the second the mother's. For example, the novelist Perez Galdos, commonly known as Galdos, since it is a less common name, should really be known as Perez, which would be rather boring.
President Aznar, is actually Aznar López, while president Zapatero is Rodríguez Zapatero.
Furthermore, the number of Castilian surnames is rather limited. Thus you will come across many people with the same surname. Pérez, López, Rodríguez - already mentioned above, or González are particularly well-known, not just because they are surnames of presidents and other famous people.
It all makes for an interesting life when booking people into a conference!
For the full low-down on Spanish surmanes, take a look at the Spanish Statistics Institute lisitng.