There has been some gnashing of teeth over the circumstances, or rather the outcome, of this article on .380 ACP effectiveness that I originally heard about through Uncle's site. There's a piece at Too Lazy to Fail that addresses some of the concerns and it has merit. Give it a read.
I wanted to expand further and say that there are many reason why some people don't carry large handguns, so you have to think of why you carry a handgun in the first place. Because it's convenient, handy personal protection.
Remember the first rule of gunfighting: Have a gun. I ridicule the generic arguments over what calibers are effective because it's all macho posturing. Caliber effectiveness goes beyond the size of your threat, the depth of its chest cavity, the layers of denim, or the distance to the target. Your personal circumstances play the largest role in determining what works best, and if you can't afford to practice with .45 ACP, or your mom would freak if she discovered your concealed .454 Casull, then downsizing is a typical option. It's hard to argue that a .22 Long Rifle is inadequate if that's all you have with you.
I have heard of similar outcomes as the one above with just about every cartridge. I read an article in a gun magazine recently, perhaps from Mas Ayoob, where a home intruder was shot in the face with a .44 Magnum from a Ruger SuperBlackhawk. The bullet impacted just below the left eye socket, but the intruder lived to tell the tale. I have heard about a home intruder hit in the face with another .44 Magnum, this one from a Marlin lever action rifle, and that scumbag lived as well. I know an individual who survived a .38 Special round through the brain from muzzle contact. None of these rounds are considered inadequate. We hear stories all the time from Iraq where multiple rounds from a rifle failed to end the fight.
You have to carry what is realistic for your environment, and be as proficient as possible. That is one reason why I'm such an advocate of 9mm, because I can afford to practice much more than I can with .45 ACP.
The size of the weapon is a big concern. I can't carry at work because none of the guns that I own are small enough to conceal with my attire. In a post below you will see my compact .45 ACP 1911 that is way too big for me to carry at work. The same goes with the Glock 26 and Kahr PM9. I would be better off carrying a tiny .380 or .32 ACP than nothing at all, and that is something that I will have to think about.
My point is to not get discouraged over your choice of caliber because of the outcome of one shooting. Carry what works for you all the time.