Some of the "rumors" are sticking because some of the denials aren't holding up to scrutiny. Things like the excuse that his grade school paperwork shows him as a muslim was a clerical error.
It was Pastor Wright who "brought" Obama to Christ. Before that he was not a Christian. His fathers were "non-practicing" muslims. I seem to recall reading that his grandparents (who raised him) were atheist.
Pastor Wright is himself a former muslim who associates with Louis Farrakhan and the Nation of Islam. The public has also heard the types of sermons preached by Wright. Very little about Christ in there.