I'm actually really good about "turning it on" or "turning it off" in regards to swearing. I have the mouth of a barbarian when around very close friends and family. If my grandmother or my kids are around, I have the tongue of Mother Theresa.
I think it's good to have moments when you swear. It's liberating and freeing, and if you NEVER swear around people, they know that when that accentuated "FUCK" comes out, something drastic has happened that has caused you great alarm or great harm. Its the verbal equivalent of yelling "Fire!" in a crowded theater....you save it for when that moment arrives.
I don't think it's one of those things you can COMPLETELY turn off. If you can turn it on and off your set - my problem is the lines have blurred - I swear in all situations... we'll see how it goes!