When you pause to think about it, it's "religulous." Atheists/agnostics know more about religion than anyone, including the religious!
A recent study by the Pew Forum on Religion and Public Life found that Atheists/Agnostics know more about religion than any other demographic--even more than the religious themselves! Jews and Mormons round out second and third place (although technically it's third and fourth since atheists and agnostics are technically different minority groups even though no such distinction was made in the poll). You can read the full report of the study in PDF here and view the questionnaire here.
I took the easy breezy quiz offered to see how I stacked up against the average and scored a 93% getting 14 out of 15 correct. That is 97% better than the population as a whole. Not to make excuses, but I would have had a perfect score except for the fact that the website kept timing out and I had to keep refreshing the page and re-clicking the answer dot... and the one time I forget to fill it back in the darn thing saved my answer wrong. But oh well... it's not like they asked anything challenging--as the questions were very basic. You can take the related test quiz 'How Much Do You Know About Religion' yourself and see how you stack up (remember no cheating via Wiki).
The moral of the story? "If you want to know about God, you might want to talk to an atheist."