Most of us were told in school never to end a sentence in a preposition. If that’s true, why do so many people do it? When I hear somebody end a sentence with “at” it is like I’ve just heard fingernails screech down a chalkboard. “Where are we having dinner at?” ACK! In this case, “at” is a completely wasted word; it would be much more correct to say, “Where are we having dinner?” Lose the “at” … please :)