I swear a LOT. I mean, I have the dirtiest mouth you will probably ever find (as for a dirty mind...well, let's just say it's dirtier than Mother Earth). I don't mind seeing swears in writing, as long as it's not constant. Simon vs The Home Sapiens Agenda has the occasional bad word, but they overall make the story better. Personally, though, I don't like swears in my writing. I'll cut it short or replace it with a more G-rated version. Even on LV I usually write a post, then go through and edit all the swears out/censor them. So in terms of bad language, here I'm the opposite of what I do in real life. In my fanfics I will have characters cuss now and then, but censor that too. And it all depends on a character. My OC does swear quite often, but I try not to focus on her sailor mouth... #MissingNo
It mostly depends on the situation and characters for me, but if I do insert a couple of swear words in my writing, it'll be the light-ish-er ones, the ones that 13 year olds these days would already know (but seriously, kids these days are scary...). Alternatively, I'll try to use even softer versions of them (is that correct? softer?) like 'dang' or 'heck'.
A lot of it depends on the characters and scenarios. Occasionally I might put in a swear word in the extreme, but I've also done someone who cusses excessively and people disliked that. So some characters I have will be more foul mouthed than others, but I will state in specific chapters or parts where strong language is abundant.
I stay away from curse words in my writing. I absolutely despise them as I see them as poor replacements for much better descriptors or emotional conveyors. Also, since I write in worlds with only Pokémon, using curse words from real life sounds awkward to me. As such, I use phrases that Pokémon would use--like, "Oh Arceus!"--in my story.