The Tueller Drill has repeatedly proven that an attacker with a knife can close a distance of 21 feet in 1.5 seconds. That means you must be able to draw, aim, fire, and hit your target in a way that stops his motion in under 1.5 seconds, or you're getting stabbed.
Carry Conditions
At March 21, 2011 at 11:58 AM, 
Goober
Or, you could just carry a wheel-gun and end the entire discussion. No safety to have to mess with; no worrying about round-in-the-chamber or not; your "malfunction drill" consists of "just pull the trigger again".
Yeah, I know, you won't have as many shots to send downrange as you will with an auto, but the statistics show you most likely won't need any more than four rounds, anyway, and a speed-loader is easy to carry in your pocket if you end up being one of the one-millionth of one-percent of the folks that find that more than 6 rounds is necessary to fix the situation you find yourself in.
If you notice you are using the correct shooting form it means you arent moving fast enough and are about to die.
back peddle, draw, back peddle, shoot and continue. 21 feet is 1.5 seconds, if you can add an extra 14 by running backwards as you shoot, you can greatly increase your time. (yes I consider .7 seconds a great increase when its about 50%)
At March 23, 2011 at 6:49 PM, 
Johnnyreb™
ASM826 - Absolutely. And in this situation the attacker is too close to effectively draw and fire without creating some distance between you.
Tango Juliet - Uh-huh, and using an IDPA timer/holster it takes me around 1.5 seconds to draw and fire a double tap. And thats anticipating "the beep" and not wearing a cover garment ...
Goober - This scenario is for those who carry single-action as opposed to double-action semi-autos. Those that aren't comfortable carrying with a cocked and locked 1911 or a partially cocked Glock. It's a moot point for those who carry double-action since it's basically "point and click". IMO a light hammerless snubbie in a jacket pocket is the ultimate concealed handgun ... just fire through the pocket.
Arthur - LOL, I heard a young lady from Florida recently used her magic pink snubbie to good effect ...
Anon - That would be the logical conclusion, especially in this scenario.
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I absolutely believe you carry with a round in the chamber.
That being said, do not draw in that situation! Pull back, keep your footing, turn away, deal with the knife. If you stand and draw, you will be stabbed to death every time. A bladed weapon in close like that will be a fatal attack. You have to have some means to gain separation and then draw.