I was using my Grex pinner to attach 100 plus feet of small cove molding on a remodel job. The Grex doesn't have a nose safety, instead it has a two piece trigger. You squeeze the safety with your second finger and the trigger with your index finger. Well, I got in the bad habit of holding the safety down between shots. As I was moving to position the next pin, I bumped my elbow on a nearby soffit and that caused me to squeeze my index finger reflexively and I fired a pin in mid air. The gun was about six inches from the trim and the pin buried itself a good 1/2 inch into the poplar trim less than half an inch from my other hand, which was holding the molding. I'm pretty sure that pin would have gone right through my hand had the aim been different.
Needless to say, I have been much better about releasing the safety before lifting the gun...