I can talk at infinte length without using any curse words, foul language or suggestive dialogue, because that's how I was raised to talk with people you respect.
If, however, the people you're talking with are just your buddies, or your well-known coworkers, or even family you know are cool with it, then "respect" is not a factor. You are communicating with them on a level they are the most comfortable with. It's like wearing a tux at a formal occasion, and jeans & a t-shirt when you're just kickin' it. It all depends on the situation.
But that's just my opinion.
As for me, I curse A LOT when i'm with my friends and such, and I can be extremely vulgar. They curse, they feel comfortable with it, and they appreciate that I can feel comfortable enough around them to talk as I please- and I, them.
EDIT:
I also swear a lot during sex, and the intensity of my orgasm can be measured in the amount I curse. My ex (the one i was with for 3 years) knew this very well... the best orgasm I ever had, I was yelling and cursing (the thing lasted like almost a minute, no kidding) and towards the end of the wave, I yelled out, "YOU FUCKING CUNT!!!"
I NEVER use the word cunt. I hate it. HATE it. She knew this. (I also do not like the word 'twat', but that's besides the point)
She took it as the biggest compliment she's ever been paid. I freaked for several minutes after I said it, fearing I had fucked up irrevocably.
Next morning, I got a wake-up BJ, and she made me french toast. I fuckin LOVE french toast.