You've seen that in text messages, heard people actually say it out loud, but do you really know what it means? Now before you attempt to justify yourself with "I meant Oh My Goodness", let's just realize from a Biblical perspective, you don't have any goodness, God alone is good, so you still end up talking about Him.
Now then, the Third Commandment says you shall not use the Lord's name in vain, this is called blasphemy, so let's determine what exactly this means.
First, we should recognize the difference between "God" and "god." Some may say that "God" is not His name, so it's not really blasphemy. However, with capitalization, it is indeed referring to the one and only true God revealed in the Bible and not some generic god invented by man.
Blasphemy is the use of God's name, including "God", "Jesus Christ" or "Lord" irrelevantly, without due respect. Consider this: If I were to use your mother's name as a curse word, would you have a problem with that? Most people would. If every time I wanted to express disgust, I would use your mother's name in addition to a few other four letter curse words, would you be offended? How much more should the Creator of the universe be offended when His own creation does this constantly out of rebellion and ignorance?
And to use "God" as an irrelevant expletive (as in omg) is the same offense. Now that you realize exactly what it is that you are doing, I do hope that you'll stop.
And I hope that you won't stop at a Hallmark store and buy one of these "cute" little blasphemous decorations that I saw the other day.
What is this world coming to? I'll tell you, it's coming to an end. No one knows exactly when that will be, but know this. 150,000 people die every day. That's two people every second, off into eternity. Are you ready?