The Pew Forum has just released the results of a survey of Americans' knowledge of religious beliefs and practices. They provide a sample quiz you can take to see what you know and how you compare to the rest of the population who took the survey.
The most striking thing to come out of the survey is that persons self-identifying as atheist or agnostic scored better on average than persons self-identifying as religious (regardless of the religion they profess). Jewish respondents came in a fairly close second, followed by Mormons. Mormons and white evangelical protestants did best on the Christianity questions.
A full report (which I have yet to digest, but which may prompt follow-up posts) is also available. A cursory review of the results shows that Americans know almost nothing about the Great Awakening (either first or second) or Jonathan Edwards. Almost half believe that "do unto others as you would have others do unto you" is one of the Ten Commandments. And, despite Charlton Heston's best efforts, many people do not know that Moses led the Exodus out of Egypt.
