In the last Presidential election there were a lot of talk about Obama being a secret Muslim. I don't think he's a Muslim, but I don't think that he's a Christian either. I think he's most likely an atheist or an agnostic, but grew up going to church because he's involved with his community.
What do you think his actual religion is. For definition let's simplify each religion as the following:
Christian: believe that Jesus died for our sins and that if he did not, we would not enter heaven.
Muslim: believe that Mohammad is the last prophet of God.
Atheist: believe that there is no God or that the probability for God's existence is so slim that there is no point in entertaining his existence.
Agnostic: is uncertain whether our not God exists. The degree of his belief in God's existence is irrelevant, but he would not consider himself an atheist.