Yes, when I was 17 came across a group of "interesting" looking characters while deer hunting on the family property. They were not pleased when I showed up and told them to "get their asses off my property", but upon seeing I was carrying the .270 I use to hunt with, they did in fact leave.
This is a hard one to answer.
The answer is no, if I don't count my military deployments or my time on the streets on patrol.
Ive never had to shoot anyone on the job (minus the 5 mortar rounds lobbed at a group of 10 Fedayeen Loyalists in Iraq). But there is no way of knowing whether or not my presence as a known gun carrier has prevented someones planned act.
Of the times ive been involved in use of force incidents, Ive managed to restrain the suspects without using threat of lethal force.
Nope, but then again, I don't put myself into situations where I'd ever likely need one.
One of the first things I tell all my students (in defensive handgunning/self-protection classes) is that 90% of self-protection consists of general security proceedures (ie locking doors) and awareness/avoidance actions (ie I notice two suspicious persons loitering in the stairwell, so I avoid them and go a different way).
Use of force is a last resort, and using a firearm is even moreso a last resort. There are, however, situations where nothing but a gun will give you any reasonable chance of survival, let alone coming out "intact".
And there are situations where even having a firearm won't leave you intact. So what? The fact is, the overwhelming majority of situations, you will never find yourself needing a weapon so long as you take reasonable care. The very, very few where it may be of some use, it's also likely that it'll get used against you.
I'd rather just avoid the situation altogether.