I'm sure that most here have read more than a few posts from @lklawson about ammo capacity in your primary weapon. Many have probably also read of his high regard for TTAG.
Well, TTAG put out an article with a video wherein a deputy had a run-in with a nutty college professor-lookin' dude, and it took most of a magazine to put the guy down. The article discussed the fact that not everyone goes down all that quickly and that there is something to be said for some extra capacity in your carry gun.
A word of caution: The guy filming it was pretty obnoxious.