I think most people have probably heard about the religion quiz set up by the Pew Forum that the majority of Americans failed, and which showed that Athiests and Agnostics seem to know the more about the various religions of the world than most people who practice an organized religion, and that Catholics know the least among various groups. Not a surprise, if you ask me.
None of it is a surprise to me, really. I feel like Athiests and Agnostics tend to reach the decision to believe as they do after a lot of consideration. Religions came to exist for a reason, and to walk away from believing in any faith at all is not a decision that I think anyone could make lightly. So I feel like people who have no faith in any higher being, or who believe in something, but they're not quite sure what, tend to have weighed their options within existing belief systems before getting there. I will keep my opinions on the Catholic church to myself.
It's 32 questions long, and I strongly encourage everyone to take it and see where you fall. Here's the link.
And here's a summary of the average results:
Americans overall: 16/32 correct
Athiests/Agnostics: 20.9/32 correct
Jews: 20.5/32 correct
Mormons: 20.3/32 correct
Protestants: 16/32 correct
For the record, I got 29/32 correct.