I don't profess to be an expert on this phenomenon or religion in America, but it appears to be a bunch a atheists who just like to have a "church like" experience. Yes even I have Thomas Tallis and Pallestrina CD,s. They don't appear to be anti religion or evangelical and their attitude may be summed up in Spherelinks link " "In the U.S., there's a little bit of a feeling that if you're not religious, you're not patriotic. I think a lot of secular people say, 'Hey, wait a minute. We are charitable, we are good people, we're good parents and we are just as good citizens as you and we're going to start a church to prove it," said Zuckerman. "It's still a minority, but there's enough of them now." You (posters here) may not be aware, that in the USA, atheists are now the largest group that can be legals disciminated against. If anyone disputes or would like documentation to support this contention (repeated below), "I think a lot of secular people say, 'Hey, wait a minute. We are charitable, we are good people, we're good parents and we are just as good citizens as you" Just ask and I will provide it.
In England I think a lot of people like that might go to the local CofE chuch, though they'd keep their disbelief to themselves. We have a phenomenon called "social Christians", e.g. "I'm not a 'believer' but I like the ambience, the music and the ethic". Then there are the usual, "I'm religious but I don't go to church" brigade (and certainly not on Christmas Day when they're 'too busy' at home). I believe that various humanist lodges are also spring up. Goodness knows what they get up to. The comfortable label 'agnostic' seems to be being replaced by the harsher 'atheist', probably owing to the malign influence of Dr Dawkins, who, ironically is in fact an agnostic (and, I've heard tell, considers himself a 'cultural Anglican').
I have only heard on another forum that Atheists are the largest group that can (not are) be prejudiced against. I'm not saying that in practise this is a big issue. It's in much the same vain I imagine that I can legally be prejudiced against say "red heads" or people under 5'4". I know 10 or so States in the USA have laws barring non believers from public office. But in practise no-one enforces these laws and just quietly look the other way as we quietly looked the other way when James Hewitt ran foul of the 1351 Treason Act.
Of course that begs the question of whether atheists are a "group". You do hear people talk about "we atheists" but in practice they're an ill-defined, non-cohesive bunch of individuals. All they have in common is a label they choose to give themselves. As for discrimination, it is, of course, perfectly legal, at least in England, to discriminate on all sorts of grounds, such as ability, intelligence, educational qualifications, etc. In some cases (gender) it is legal to discriminate against women, as the RC Church does (and some parts of the Anglican Communion). And it's perfectly legal for the RC Church to expect that the head of one of their schools shares that faith.