"The exact number of faithless is unclear. One study by the Pew Research Centre puts them at about 12% of the population, but another by the Institute for the Study of Secularism in Society and Culture at Trinity College in Hartford puts that figure at around 20%.Most experts agree that the number of secular Americans has probably doubled in the past three decades – growing especially fast among the young. It is thought to be the fastest-growing major "religious" demographic in the country.
There are other indications, too. For a long time studies have shown that about 40% of US adults attend a church service weekly. However, other studies that actually counted those at church – rather than just asking people if they went – have shown the true number to be about half to two-thirds of that figure."
Guardian.co.uk, Saturday 1 October 2011
Feelgood article in The Guardian.