Misusing God’s name

Many people these days say, "Oh, my God." Is that not taking God's name in vain? Thank you.

Yes.  God did not reveal his name to us so we could use it as an interjection when we are surprised, upset or angry.  God commanded (Exodus 20:7) that people not “take the name of the Lord thy God in vain” (King James Version) or “misuse the name of the Lord your God” (New International Version).  The common exclamation you described is a misuse of God’s name.

Our Catechism reminds us from Scripture that God has revealed his name to us that we might pray to him, praise him and give thanks to him.

Our Catechism also reminds us from Scripture that Jesus forgave our sins against the second commandment by keeping that commandment perfectly in our place and by suffering the punishment our sins against that commandment deserved.  That surely is reason and motivation for using God’s name properly.