Depends on who I am around, the situation I am in and the topic I may be discussing.
Around friends and co-workers, I would say I'm at about a 7 (I'm not proud of it).
When I am driving in my car by myself, I would say I am an 11. I have 'issues' when I am driving.
Around other people and when I am out and about mingling with the general public, I would say zero if I am alone, but in my mind and my thoughts, I am still cursing at about a level 2.
About a 3 If I am with my wife - we love people watching and talking about the number of idiots that surround us, which inevitably leads to us using a few swear words during our conversations.
When working on a PC (be it a hardware related problem, or software related problem) and I am having a particularly difficult time troubleshooting and solving the problem (rare for me), I would say I am at about a 7.
On the rare ocassions I find myself in a Church, zero.
Around Grandma (or elderly people in general) and childred, zero.
Around my father, 4.
There are many more situations I didn't address, but you get the picture.
So I guess that would put me at about an average of 3.78