In real life I have no aversion to using strong language if the situation calls for it. I mean, if a boss in a game is annoying me, then I'll swear bloody murder at them ("Damn you biatch, just ******** die already!" wink . But I don't really swear for the hell of it, because then it sounds stupid and loses whatever impact it might have had. When I swear a lot it's usually because there's a reason for it, or I use nonsensical swear words. Everything from 'bloody hell' and 'goddamnit', to 'fudge', 'crapulence' and even 'crud monkeys'.
As for characters, it depends on their personality, but as others have said I go on instinct and try to create swear words that fit the context. If my world has no notion of a hell or god, then I'm not going to have them say "goddamn you to hell". Instead they'd say "[insert deiety] curse you" or something like that...