The legalities of what you do will vary from jurisdiction to jurisdiction, so I won't make a comment regarding that other than to advise that you check with your state and local laws.
My personal approach, however, is to never start a fight, always do what I can to avoid a fight, but if I'm attacked do WHATEVER is necessary to end the attack. Under most circumstances, I'm not going to pull out my gun and shoot them, but I'm going to start off on the extreme end of the scale and work my way down, so to speak. I'm going to bite, poke, gouge, punch, knee, kick, pull, head-butt, grab your sack and wring it like a wash cloth, use a rock/stick/pen/keys or anything else I can get my hands on.
If you've done everything to avoid the situation, any attack is potentially life threatening, however; once the attack ends and the attacker A) runs away, or B) is incapacitated to the point that they can no longer attack, I stop defending myself. It's actually kind of common sense.
Where I live, it's pretty lenient as far as deadly force; even in a civil court. Here you are within your legal rights to shoot someone through the door of your house without even seeing them if you can reasonably show you had reason to feel threatened. Believe me, I know of cases when such a thing has happened--the person banging on the door was unarmed--the homeowner blowing them away through the door. No arrests, no convictions, no civil liabilities.
Common sense and the "law", often times, have no connection.
samuraiwarrior: Federal permit to carry a concealed weapon? Hmm, not in the US, you didn't.