I am 25. (Although I still haven't gone to college and won't until some time next year due to financial issues.) I have been (casually) researching terminal ballistics for nearly 13 years now. That's nothing official, and the research was casual, but since I've been at it for 13 years, I'd say I likely know more about terminal ballistics than the overwhelming majority of the people here. I've spent so much time researching this that I've actually created a working system for (very roughly) calculating damage and the amount of such neccesary for lethality.
Now that that's out of the way, let's move on to the topic at hand.
If you've ever watched an action movie or played a video game, you've probably seen a lot of glorification of the use of firearms to put bullets through the brain, and probably soaked up the attitude that headshots are magical, insta-kill shots that any weapons can perform. This is fundamentally stupid and really pisses me off. I'll try to thoroughly explain why.
1. Relative size: the brain, the only part of the head you'd want to shoot, is a relatively small organ, and if you miss it you do no damage at all.
2. Importance: the majority of the brain is redundancy and wasted space. This is what you're likely to hit.
3. Protection: the brain is protected by the skull, a thick, hard bone rounded on all sides. Even rifle rounds tend to ricochet off it they hit at a bad angle, and smaller rounds, such as birdshot and some pistol rounds, will not penetrate it at all regardless of angle.
4. Damage: headshots do little real damage. What they do is reduce or disable bodily functions and reduce the amount of damage neccesary to induce shock. (Usually by enough to send the target into shock immediately, but not enough that they can't recover with proper medical attention.)
5. Other targets: every organ in the chest is a better target than the brain, as are most major blood vessels. The lungs are huge, easy targets that do more actual damage than a headshot, and not by a little; The liver presents a smaller target, but still does more damage through sheer blood loss; The heart is pretty much an instant kill, as any human shot with anything bigger than a .32 will be dead before a doctor can get to them; and the aorta, a fairly large target, will cause death by exsanguination in less than a minute.
6. Headshots are inhumane: due to the way they induce shock but do little damage, headshots are a slow, cruel way to kill somebody. When you shoot somebody in the head, they might hit the floor twitching, but since you didn't do any real damage you're relying on the shock itself or a loss of bodily function to kill them, both of which are extremely slow. To make it quite plain: they will be paralyzed, and hopefully unconscious, but at best they will not die for hours, possibly days or even weeks if they get medical attention. (They could be kept alive indefinitely, but sooner or later somebody is going to pull the plug.) Compare this to a shot through the heart, which kills them flat out in less than a minute with anything bigger than a .32, and is an easier target than the few portions of the brain that would actually prove lethal.
In the end, aside from "style" there are only three reasons to shoot somebody in the head:
1. You need them to hold still after you've shot them several times in the chest.
2. You need them to stop moving now, and don't care if you actually kill them or not.
3. You can't hit the chest.
If anybody wants to try and fight this with a bunch of pointless headshot wank, be my guest, but you're argueing with the well-informed opinions of every military, police or civilian firearms instructor, trauma surgeon, sniper and layman with a bit of common sense on the planet, not just me.
Title changed to reflect the HOSing. -- LadyT