Jon Rowe is guesting on Sandefur's blog this week and has this essay on the dual influence of Christian and Pagan sources in American history. I think he nails the issue almost completely. Like him, I thought the ACLU's lawsuit threat against LA County over their seal was pretty silly. But in most cases, the ACLU is right on church and state issues, despite the often hysterical overreactions from the religious right.
Slightly off-topic, but I really dislike the use of the word "pagan" to describe anything non-christian. To me it holds the same type of disrepectful overtones as the world "infidel" does to non-muslims. Pagan is a brand of theistic belief, and should be used for that purpose only, in my opinion. /rant
I think it's equally important to point out that many of the Founding Fathers were Masons and Deists -- two groups which contemporary conservative evangelical Christians would not consider to be Christians. It's really quite odd, then, when these same individuals come esposing a Christian Nation theme.