(Hi people, I was the beta who liked actual swearing being used. :P)
Swearing seems to be a no-no in the PPC in general; strong language gets you automatically kicked from the IRC, and the Constitution has this to say:
"...[N]o cursing, no graphic violence, sex or whatever.""
It's noted that this is to keep the community worksafe and family-friendly, and to be fair the Constitution goes on to note that if a story has such content there should be a fair warning (as opposed to, say, a flat-out ban on any such content), but I think it illustrates why we take the approach we do, with fandom-based cursing (though as pointed out by other posters, if a character's actually from that continuum it makes a lot more sense they'd use those words, then you have cultural factors, etc. etc. :P) and Creative Curses and the like.
I'm of two minds about this - much like excessively gory violence or explicit smut a) isn't really something most in the PPC want to write and b) sure as heck isn't something a reader wants flung at them without any kind of warning or way to know it's coming, gratuitous language comes off as childish and tiresome, and I'm sure nobody here's interested in the extreme approach, where f-bombs, s-strikes and various slurs are tossed around seemingly every other word. On the other hand, when people talk, swearing is a thing that happens, and there's not much use acting like that's not the case - and in particular, I've honestly never liked our "Creative Curses". Not only do they come off as overly cutesy, convoluted and euphemistic, not one of them (except "Flaming Denethor" maybe, but who really wouldn't just say something more conventional in that kind of context? Also, it sounds more like a drink, one I'm pretty sure is actually served in one of HQ's bars...) strike me as something anybody would ever actually say - sure, a lot of dialogue writing doesn't perfectly match how people talk in reality, but trying to picture someone blurting out "Jadis in a block of ice!" or "Reinforce Eins (?) in a sweater!" every time they're surprised by something takes me right out of the story. I mean, try it out - try saying "Glaurung!" or "Flaming Denethor!" or one of the others right now like you're angry or startled, I bet you sound foolish (no offence) and don't have as much impact as using something stronger.
Okay, that was a big paragraph about fictional cursing, I swear it doesn't actually get me that worked up. :P Obviously it's all down to character and how they would talk, I think we'd all kinda eyebrow if the SO started talking like a drunken sailor for example, but I kinda feel like if it's a situation where the writer feels language would be warranted from the person swearing they should at least not shy away from it - of course, if silly and euphemistic is what you're going for, go nuts, and like I said it should fit who they are and where they're from, but still.
As for the last part of the question... I'm actually gonna have to think on that, I have so many agents and concepts drawn up I'm sorta losing track. Most of mine are from various periods in World One and use the according language, though from mine in other continua they stick mostly with the vernacular from their homeworlds of course (one big Star Wars fan in my bunch likes to use swearing from the GFFA though - mostly nondescript Mando'a or Huttese or stuff like "kriff", and I'm writing a Firefly mission with people who might stick with the tradition of censor-dodging via Chinese). Most of them don't swear particularly often though, either due to being too formal, not being easily moved to cursing, or just a sorta general affable and not-easily-roused demeanour, though in my last mission (Jeez, that was three years ago now...) Miriam did cut loose a good bit and called the Sue a bitch a few times; a lot of that was freaking out over how the continuum had been twisted around so much it literally began tearing itself apart under the strain put on by the Sue, though. I might have to get back to that part of the post with something more concrete.