An interesting Pew study found that American atheists and agnostics had a better overall knowledge of religion than did believers. You can read the longer Pew article and shorter L.A. Times overview here. Not surprised by any of this, not even the finding that Mormons knew the New Testament better than evangelicals.
The study did not break out UU's as a group, but it would be interesting to see where we fit. I would guess that many non-born-and-raised UU's would do well for the same reasons as the atheists and agnostics. It would also be nice to see how those who grow up in UU RE compare.