I shot 40+ this past year. About half that the year before. Of those, I've only had one that I thought was actually charging me. I shot him in the head at about 15-20yds but didn't get the brain and he went wild, jumped into the cedar breaks, then came out full steam right at me. Two more quick shots and he was down. He was so close after the second shot my hand immediately went to my pistol. That's the only one. I've had lots run at me, but I believe they aren't sure where the danger is, and I am usually standing on a game trail, so it's a natural escape route for them and I'm just in the way. Most of the time when they actually see me, they turn...unless I shoot them first.
Bottom line, I think it's rare for a hog to charge....at least a lot more rare than many would lead you to believe.