As there is now a movie out right now about the US-coordinated assassination of Osama bin Laden, I thought I would come back to what I found to be the problematic response of many Americans to the death of bin Laden. When the news was announced, there was a rather morbid celebration in the US, creepily evocative of the video footage that we often use to show the anti-Americanism of the "Arab street."
It brings me to what I believe to be a vital distinction--that between celebrating an action versus celebrating a state of being. One cannot help degrading oneself a bit when one chooses to celebrate such an assassination, even if that person were particularly terroristic or tyrannical. The moral uneasiness stems from the fact that, when celebrating this, you are celebrating the act of murder. (One can strengthen that further by highlighting that one is celebrating the act of murder in a case not tied to self-defense.) By doing so, you are then, whether intentionally or not, legitimizing the act of murder in cases not related to clear self-defense.
Celebrating the act does, however, differ from celebrating the state of being. In other words, one could claim to be happy to live in a world in which Osama bin Laden no longer exists. In that case, the reason for your contentment is divorced from the act itself--you are by no means condoning the act. You are merely acknowledging the value of the non-existence of a threat to one's (or one's nation's) sense of safety and security.
I should probably flesh this out a bit more; regardless, I think it is an important moral point that is too frequently overlooked.