Unfortunately, I've been in several life or death situations. Like Lloyd said, if you took the time to think, you probably wouldn't survive. It's in those cases that you tend to fall back on pure instinct, and reflexes.
Dakotashooter's point is dead on too. A lot of people just aren't proficient enough with a semi-auto when it comes to an actual high stress senario. A revolver is as simple as it gets.
Myself, I could use just about anything, but I prefer a Single action. I know all the arguments about fire power, reloading, etc., but honestly, unless you're in an actual war, or combat situation, those arguments just don't apply. I've personally witnessed several "actual" fire fights, and been in a couple+ myself(got the scars to prove it). I've yet to see anything like whats depicted on TV, or movies. In most of the cases I've seen, very few shots were fired. The worst was when I was shot in my left thigh, and he fired about 5-6 "aimed" rounds from a protected spot while I emptied a 15 round magazine kinda wildly in an effort to exit the area. 15 rounds did no more than 2 or 3 would have. I was just scared to death(19 years old), and basically wasting my ammo, but it saved my life none the less.
Other than that night, I honestly don't think I've seen more than about 3 to 5 shots exchanged combined from either side. It's usually over so quick that unless you're right in the thick of it, you're still trying to figure out what's going on after the shooting has already stopped.
I know that it's common nowdays to carry a semi-auto for protection, but I'll take my tried, and utterly reliable 357 Blackhawk over any gun except maybe a good reliable carbine, or shotgun. I know that within 50 yards, if I keep my cool, I can absolutely finish any attacker with only one of my 6 shots. If the ranges are normal(5 to 25 feet) he's pretty much toast because I'll be shooting instinct(pointing only), and that comes so naturally that reflexes take over, and I know I'll be connecting with my shot before I really know what I've done. That takes us back to Lloyd's point...