I probably swear more in character, than out of character.
Unless I'm gaming with those who would be offended by it, then I leave it be.
And I just use normal american swears in D&D, which is maybe a little silly, but no one seems to mind. It just feels a lot better to me, saying a normal swear, than cursing the darkness. Well, generally. Depends on the game!
Modern games, no compuncture, there's just a lot of swearing. What else do people do when they're getting murdered, anyway? Not that it's better that way, it's just how many modern games I've played have gone, and how people have been happy with it.
It mainly just depends on the group.
However! I did play in a star wars game for a little bit, where the DM proclaimed, hey, there's no swearing in star wars. Nobody there was offended by swearing or anything, it was just a style issue.
Hmm. Maybe I should make it a style issue for my own D&D games. Finding a better in-game swear might be more fun than just having my character mutter something colloquial.
But, there's also just something about having a character use a term that everyone can connect to, and follow what the character means. ah well, I'll try the other, I think!
Agreed on the swearing in fallout, though. It just wouldn't be fallout without it, really.