Words, words, words!

I grew up in a family in which "S.U." (shut up) were bad words.  Sometimes we could get away with the initials and not have one sibling or another tell on you.  Somewhere around high school or college, we started to use the word "crap."  It was not met with great enthusiasm by my mother.  Now we use it fairly freely in speech while remaining aware it is not the most polite word.  I can count on one hand the number of times I heard my mother utter a four letter word, and it was almost always after smashing her toe into something.  In our family, we used polite words.

In the movies, on tv, and amongst my peers, there is a much broader range of vocabulary to be heard.  I have wrestled with this idea of polite language versus cussing or swearing.  I have friends who openly swear with a clear conscience and those who won't even say "Oh my gosh."  Biblical Counseling Guru Paul Tripp has some great thoughts on the subject.  (If you like this, check out his website or any book he has written.  I recommend Instruments in the Redeemer’s Hands: People in Need of Change Helping People in Need of Change.)

How do you define what language is appropriate to use?  Is it merely cultural or also Biblical?
Also, do you distinguish between cussing (bad words) and swearing (using God's name in vain)?