Said I'd plonk this up, so I am. I've found that I have virtually no problem with other people swearing. You could swear at me using the dirtiest and foulest language you've got until you're blue in the face, and I wouldn't really care that much. I'm not going to restrict your "freedom of speech" that is so valued by people.
But I tend to regulate my own speech a fair bit. Generally, I've found, according to the expectations of the people around me. Meaning that most of the time, I won't swear very much at all. But when I'm with someone who swears a lot, I'll do so a bit more. When I'm by myself, I'll swear actually fairly frequently. There's some words that I just don't use, but I've surprised myself at how frequently I'll swear when I'm alone at home.
When I'm singing, I'll very much pay attention to what I'm saying/singing. I don't write swear words or sexual references into any of my songs - to the degree, in fact, that I recently wrote out the worst word I have used (groin) in one of mine. And if I play a cover (which I've only done twice; but take it as a hypothetical), I either wouldn't use a song if it had swear words, or would change it. I know, that sounds bad, changing a song that's not yours - but I think that the impression you present is very important, and I don't want people after my gig thinking that I swear a bit, whether they think it's good or bad. I don't want people getting a wrong impression of me, basically. Plus, there's often kids at the gigs I've played at. :P