The Volokh Conspiracy has an interesting post about the Constitutional right to lethal self defense:

Lethal self-defense is so broadly accepted that courts have rarely had occasion to confront grave restrictions on it, and thus haven't squarely decided its constitutional status. Some lower court opinions have said that there is such a right, and a recent four-Justice plurality opinion -- authored by Justice Scalia, usually no friend of unenumerated constitutional rights -- suggested the same. And the Court's unenumerated rights caselaw provides a strong case for recognizing a presumptive federal constitutional right to self-defense.

I find this interesting from an intellectual perspective, but don't really find that it affects my life.  Not because I think I may never find myself in a situation where I would have to think about this, but rather because if I found myself in such a situation, I wouldn't have to think about it.  Whether some person in a robe says I can do it or not... If my life, or more importantly the life of someone I love were in danger, I wouldn't hesitate to use lethal force if that's what it came to.  If I have to spend the rest of my life in jail so that someone I love lives, then so be it.