When a Christian says something like "Burn in hell Osama," they mock the gospel of Jesus Christ. They are telling the world that our Father in heaven doesn't desire that all men be saved. They are telling the world that Jesus taught that we should pray for revenge upon our enemies. They are telling the world that the angels rejoice when a soul is lost. That is not the message of the Kingdom of God. That has nothing to do with Christ's mission of redemption in the world.
I don't like Osama Bin Laden. He was a mass murderer. I do not doubt that what happened to him was deserved. But that's the end of the story. His story didn't begin that way. He was a human being made in the image of God. I've read that as a young man he was known for his piety and was a respected member of his community. But somewhere along the way this world twisted him.
I can only feel sadness for what he became and the way his life ended. I'm NOT trying to absolve him for his crimes. I understand why the U.S. government took these measures, and I'm sure the world is a better place without him. But when a human being made in the image of God ends with a bullet through the head, no matter who they are, that should be a sad reminder of the brokenness of our world, not an occasion for celebration.