Article:  Interesting study of religious affiliation in the election demographics.

Executive summary: While Romney held a commanding lead in Protestant votes, and Obama squeaked ahead on the Catholic vote (but losing it in some states), the "unaffiliated" category went overwhelmingly for Obama and provided another statistical piece in the election puzzle. "Unaffiliated" encompasses atheists, agnostics, and nondenominational believers.

Opinion: This category is one that's growing substantially over the generations. Catering to religious fundamentalist social views may work in some areas, but overall, it's a slow but marked decay of a strategy.

I think we know which party has the bigger tent.

My guess is that the atheist and agnostic segment of unaffiliated is about as big as their portion of the population.