Well...there was a similar poll very recently by the Pew Research Center again. About how much Americans know about religion, and strangely, atheists scored higher than Catholics and even Evangelicals. Granted, several of the questions were about other religions than Christianity, but that still seems very surprising that so few people would know the answers to these questions.
Here were my results on their online quiz. I scored a 100%...
And here is the online quiz if you would like to take it yourself: http://features.pewforum.org/quiz/us-religious-knowledge/index.php
