Does Elayne ever leave her potty-mouth stage?
Sanderson's "Lord Ruler" was actually one of the made-up expletives I didn't have a problem with. I'm not talking about Sanderson's work in particular here, but often the made-up expletives kind of bug me; I think it's just a bit hard to come up with something that doesn't sound lame. The reason "Lord Ruler" worked for me as an expletive is that it really goes to show just how the people of the Mistborn world regard the Lord Ruler; not just a king, but a god.
While it's always nice to see aspects of an imagined world's culture shown off in whatever aspects you can manage it, swearing included, there's only so much world-building that I'm willing to sit through for the sake of a swear word. Basically I'll let an author get away with made up swearwords if they have some context that isn't just there for context's sake.
Books that mix real curse words with invented ones end up making their invented swear words look kind of weird.