Check out this Breitbart News article which reports that the irreligious voted overwhelmingly for Obama. Unchurched voters were more common than formerly thought; this group is growing.
Although the article doesn't say so, the GOP's obvious association with the religious right - the evangelicals - makes them anathema to the irreligious. I fear there isn't much can be done about this reaction, the GOP needs the votes of the social right.
Here is National Public Radio's take on the same story. Conservative leaders need to think about what this means, and how to deal with the changes in the demographic profile of the electorate.