Growing Number of Americans Say Obama is a Muslim
“A new national survey by the Pew Research Center finds that nearly one-in-five Americans (18%) now say Obama is a Muslim, up from 11% in March 2009. Only about one-third of adults (34%) say Obama is a Christian, down sharply from 48% in 2009. Fully 43% say they do not know what Obama’s religion is.”

http://pewforum.org/Politics-and-Elections/Growing-Number-of-Americans-Say-Obama-is-a-Muslim.aspx

U.S. Religious Knowledge Survey
“On average, Americans correctly answer 16 of the 32 religious knowledge questions on the survey by the Pew Research Center’s Forum on Religion & Public Life. Atheists and agnostics average 20.9 correct answers. Jews and Mormons do about as well, averaging 20.5 and 20.3 correct answers, respectively. Protestants as a whole average 16 correct answers; Catholics as a whole, 14.7. Atheists and agnostics, Jews and Mormons perform better than other groups on the survey even after controlling for differing levels of education.”
[…]
“More than four-in-ten Catholics in the United States (45%) do not know that their church teaches that the bread and wine used in Communion do not merely symbolize but actually become the body and blood of Christ. About half of Protestants (53%) cannot correctly identify Martin Luther as the person whose writings and actions inspired the Protestant Reformation, which made their religion a separate branch of Christianity. Roughly four-in-ten Jews (43%) do not recognize that Maimonides, one of the most venerated rabbis in history, was Jewish.

In addition, fewer than half of Americans (47%) know that the Dalai Lama is Buddhist. Fewer than four-in-ten (38%) correctly associate Vishnu and Shiva with Hinduism. And only about a quarter of all Americans (27%) correctly answer that most people in Indonesia – the country with the world’s largest Muslim population – are Muslims.”

http://pewforum.org/Other-Beliefs-and-Practices/U-S-Religious-Knowledge-Survey.aspx