The Tueller Drill that you are thinking of refers to a "d'oh" observation that a police officer named Tueller made. In a nutshell, it is basically that the average person with an impact or edged weapon can close up to 21' before the average police officer can draw, aim, and fire his weapon.
As Ralph Mroz and others have pointed out, just getting the gun out and opening fire does not solve the problem and although I was not impressed with his video on the subject, it emphasizes the importance of getting off-line. Just because you put two 185 grain hollow points in the bad guy's torso does not (unless you get a mobility kill) stop his 220 pounds hurling at you like a linebacker off the line or the crowbar he is trying to bash your head in.
I think what the Tueller drill teaches us is something that we all learn in level one of Hock's gun / counter gun course: sometimes your best option for survival is NOT the quick draw, but rather an "other than gun" response. In one of the old CQCMag articles, Hock talks about "why cops shoot" and that article is also pertinant here.
Dan