Here are two comments I found by Christians on discussion boards about cussing around the intarwebz. I didn't write down who they are, but I'm sure a google search would turn it up if you're interested. I really like these.

"Everybody out of the pool. Somebody fucked it up. We need clean water and a new perspective. Wash away all the commandments we've added. It was only supposed to be 'Love God' and 'Love your neighbor' but we've been pinching loafs [sic] in the pool."

"We need to tear down the culture of Christianity that has isolated us. Start by practicing. It will get easier as you go. Every morning, look in the mirror and say shit. Easy transition from shoot. Once your comfortable, move on to fuck. Soon, you'll love the way it erupts when it rolls off your lip. I am being serious. If you are uncomfortable saying a word that has become utterly meaningless in our culture, then you are insulated from our world and you might as well wear a burka. Once you master your tongue, you'll be able to let down all those self righteous walls that have enslaved you. You'll become popular and all your old friends that slowly backed away will return. Your neighbors will come over for dinner and you can stop watching those 'Little House on a Prarie' reruns."

I was egged into writing more on the subject in response to another comment on Mr. Oak's article. No sense letting all that writing go to waste.

If you look at the context of Jesus's insult to the Pharisees, it's very clearly an insult. It seems obviously rude. Now, I admit, I haven't done an in-depth exegetical study on the greek used there ("gennema echidna"), but a word-study I have read said the phrase was a commonly used insult with a crude connotation. I do know from personal study the injurious nature of insulting any Jewish man's ancestry in the Ancient Near East context. I would suggest that it would be nearly as insulting as calling an African American the N-word. Crude or not, it certainly doesn't fall into the context of "our words being so filled with blessings that we don't have time to cuss".

You say we don't know for a fact that the Bible uses crude words, but that's simply not the case. I'll let the previous example slide. We still have the example I discussed in my original comment where Paul says bullshit. As much as any etymologist can say of a long-dead language, there is every reason to believe that this word was considered very crude and was not used in polite society. It's a cuss word, friend. There's no logical way around it.

Then we have Paul's use of the word "foreskin" which is an insult he levels at the Judaizers. A commentary I read once described the crudeness of the word as being equivalent to calling someone a "dickhead". Here we have another word that most evangelical Christians would consider a cuss word, and again it's in the Bible.

Finally, we have King Saul's use of the phrase "son of a whore". Again, very rude and very crude. Again, in the Bible.

This is the Bible that Evangelicalism doesn't want you to know about! Show me where the Bible says Christians shouldn't cuss and I'll concede and apologize. Until then, I'm going to insist that we're basing our belief that cussing is a bad idea on our Christian sub-culture's misinterpretation (and occassional misappropriation) of verses. This is why most of the Church's greatest theologians cussed in their writings. Not just in their private lives, mind you.

The Greatest Commandment (and the Second) are very important to me and they're why I'm so passionate about why Christians should cuss! I don't know any non-Christians who are offended by cussing. I know a lot of non-Christians who like to cuss.

In the first century, Christians taught new converts that in order to be a good Christian they had to eat like a Jew and be circumcised. Paul called those people dickheads. Now, Christians have taken Paul's admonition against doing that too literally. We don't teach our converts they have to subscribe to Jewish food laws, but we've missed the entire point Paul was making (Christians live by grace, not rules). In the twenty-first century, we teach new converts that in order to be a good Christian they have to stop cussing and stop drinking.

I don't see how, in love, we can pile on these polite burdens on the backs of new believers. I don't see how, in love, we can honestly tell our agnostic friends "No, I can't say that. I have to be set apart!" What bullshit! How insulting. That's never been what the Bible meant by being set apart. That's why Jesus ate with sinners.

In today's culture, sharing a meal with a prostitute or a criminal doesn't have the same connotation as it did in Jesus's day. It was a sign of identification and relation, you're saying you're their equal when you eat with them. That's why the religious people wouldn't do it. They had to prove they were set apart. 

Today, that meaning isn't there when it comes to eating meals. But we have our own version. Language is a means to identify with subcultures in our world. The geeks have leet speak, the gangbangers (and wannabes) have ebonics, the yuppies have buzz words, and Christians have plenty of our own words. Cussing is something almost every non-Christian does and too few Christians do. Cussing is our chance to identify and relate to those who don't believe, to say that we're they're equal. We're not better. We're not set apart because of the things we do, we're set apart by God's grace alone.

As far as being a poor testimony? I've been a Christian for 10 years, but I only started cussing seven months ago (after much study and thought). Even in that short of a time, I can tell you many stories where I got to show someone love because I cussed that I wouldn't have been otherwise. That's reason enough for me.