I too have wondered about the statement "If I draw my gun, I'm going to use it." I know that there will be situations where lethal force is justified but that for me would be a last resort.
Secnatio 1: If someone is pounding on the door, I will announce in a loud voice that I have a gun and will shoot him if he comes in. This will stop any opportunistic criminals and send them packing. If the person does not stop the attack, then there will be no choice but to shoot him if he comes in. I normally have my cell phone on me so I will be calling the cops and moving towards cover after I make the announcement. As for retrieving a more powerful weapon, I think this is a bad idea since the intruder may already have forced his way into your house by the time you retrieve it and may be on top of you before you have time to get it into play.
Scenario 2: This is a little more questionable since your scenario is somewhat vague. If you are in a bad area and there are few people around, then he may be targeting you. If not then you are illegally brandishing and potentially escalating the situation. I would give the guy a good look in the eye as someone else mentioned and "adjust" my gun so he knows I am armed. If it appears he is holding a weapon when he is approaching and is within 20 feet I will draw and keep the gun at the low ready position.
I am not eager to shoot anyone but I will shoot if I have to. If the bad guy runs away or backs down, then the situation has been resolved. It is not my right to remove these scumbags from the planet, as much as I would like to. I imagine my life would also be much more complicated if I didn't have to go through the whole explanation of why I shot the person to the police and the whole civil suit from the scumbag's family.
I have also given much though to less than lethal responses such as pepper spray. There have been quite a few threads lately and the stuff from Fox Labs seems to be the best stuff out there. I have also given serious thought to installing a Lasermax spring guide replacement laser that may cause a bad guy to seriously reconsider his actions. What are your thoughts on this?
The ATF should be a convenience store instead of a government agency!