Fred thanks for that info on Front Sight...I might consider going next time AZCDL does a trip now (I prefer to "try" or at least read testimonials before I drop that kind of coin).
To Citizen: a few thoughts:
-Police are different. I'm sure rules of engagement vary by agency, but for them most part LEOs can go one step higher on the force continuum when combating force presented against. Plus, and IANAL, but I'm pretty sure most LEOs are given the benefit of the doubt if it comes down to it. Has anyone ever heard of an LEO getting sued for brandishing? Thought not.
-As far as clearing your own home, well, that goes off course from the OP's hypothetical. In your house you can light your stove with a flamethrower if you want. I have gone through my house at low ready in the past when I heard a weird noise or my motion lights popped on. If it's your property you can do whatever you want. However, in the OP's post the two actors were on public property.
-On that last point about brandishing, I re-read it and what you put and I think I didn't articulate that very well. As far as your example with the car jack, that would definitely be a "reasonable" time to draw.
Here I will reference the JAM model (or AOJ as some call it): JEOPARDY, ABILITY, AND MEANS.
Jeopardy - the other person's actions or words provide you with a reasonably-perceived belief that he intends to kill you cause grievous bodily injury
Ability - the person has the ability to use the his means of attack against you
Means - the person has the means to kill or cause g.b.i
So, in your car jack situation, J (yes, a car jack will f you up) + A (the person is able-bodied, coming towards you, and capable of lifting/manipulating the jack) + M (the person is close enough or getting close enough to use it).
To be sure, no one gets free hits. You don't have to wait until you're hit once with the jack to shoot. And in that same situation I would definitely draw.
Re-reading the original thread, I guess here is a better answer: if the guy presents his knife and you draw and he just stands there, you BACK AWAY. I was re-reading ARS and Korwin's book; this could *possibly* be construed as the knife dude's "Withdrawal" from the conflict (making you the agressor).
Doesn't have to make sense, it's just the law.
ETA: Here is a pretty good article on AOJ/JAM, and a good site all around, especially for women shooters or convincing the wife/girlfriend to like your guns:
http://corneredcat.com/Legal/AOJ.aspx