For my part, I think this commandment is a sound moral teaching, so long as it's not taken as a moral absolute. Clearly there are times when killing would be appropriate, such as in self defense or defense of an innocent. Consider the situation faced by Lot, who acted the supreme coward. I'd kill, or die trying to kill, in order to prevent a rape. How could doing so be immoral?
Mike, you seem to be saying that if one views this commandment in light of all other scripture one would come away with a correct view of the moral behind it. I'm not so sure of that, since the examples the bible gives of killing are almost always either cowardly or senseless. The story of Phinehas is but one example. God's order to slaughter the Amalekites, including women and children, even suckling infants, is another. Such genocide, ordered by God himself, seems to me to obviate the commandment.
One might say that God brought a new covenant in the person of Jesus and that thus the examples of senseless killing in the OT should be ignored. I'd gladly ignore them, but the NT - and even Jesus himself - tell us that we are to revere the OT and follow its laws. Besides, it seems crazy to believe that, if God is perfect, his old covenant could have been flawed. Why was a new covenant necessary if the old one was perfect? So I'm still wondering how it is that all of the books of the OT and NT "come together" and present a perfect morality.