I suspect it's a lot. NPR ran a story last year that was interesting. http://www.npr.org/2012/04/30/151681248/from-...<quoted text>
...It makes you wonder how many people involved in these various sects are doing it out of habit or necessity rather than any kind of actual faith.
Even though that majority of the population in the US reports as being Christian. I firmly believe that if they really gave an honest assessment of their faith, a sizable portion would declare themselves agnostic (at least).
If you walked up to a hundred people on the street and told them that God literally spoke to you last night, as in - "I actually heard his voice and believe it or not, he sounded like George Burns" - spoke. How many would believe you? I'm betting the majority would think "this guy is bat-shit crazy".
And this makes me happy.