Add me to the "other" list.
I'm Sicilian, therefore, I curse. A lot. Like a sailor who should be very, VERY ashamed of himself. And, also, pretty much free of any need to censor myself in any way whatsoever.
However, I do have a few stipulations.
I never curse in front of small children or any kids whose parents I'm not close with/related to. I also never curse at work unless I'm in the office alone or I'm talking to one of the few clients that have worked with us so long they're like family. I never curse when I'm trying to make a specific point or argue a specific cause because I tend to think that it somewhat undermines the validity of your argument. Also, I very seldom curse when trying to insult someone because I firmly believe that an eloquent dig, free of four-letter words, can be the most biting.
I don't curse in front of my elders, but I do curse in front of my parents. Have since I was about 13 with no repercussions -- while somewhat strict and strong believers in discipline, they were still hippie/liberal parents who subscribed to the theories that a) cursing is pretty low on the list of bad things a teenager can get into; b) any commode mouth habits I picked up were most likely a result of their own unabashed f-bombs; and c) disrespect and back talk are no-no's, but aren't necessarily dependent on particular words.
I try to avoid specifically offending people (unless, of course, they deserve it) and will usually knock it off if someone asks me to. Also, I don't go quite full boar until/unless I know the people I'm around.
Lastly, there are several instances where I may still curse, but I'll make a point to tone down the level of vulgarity. I have two younger sisters, almost 15 and 18, and have heard the music they listen to/movies they watch/video games they play enough to know that I can be pretty relaxed in the words I say around them. But I'd never talk to/around them the way I do with my friends. I don't curse as much and I don't get quite as... well, filthy.