I just finished reading George Barna's Revolution. In some ways I was disappointed until I realized I probably was not his intended audience. I wanted some stats and research but the book is more about giving you a feel for what is happening in the life of the US church. He is trying to explain something that is happening to people who don't yet have the events fully on their radar.
Barna mentions his book Frog in the Kettle: What Christians Need to know about life in 2000 published in 1990. Barna claims he was more than 90% right in the predictions he made. He says that there are now 20 million "Revolutionaries" that have largely disconnected from formal church institutions in order to live MORE committed lives to Jesus. Some still attend a traditional church, but that is not the focus of their lives. Many others are "unchurched" people who have networked together to live out their faith in their own context.
Barna's research indicates that these 20 million (and growing) Revolutionaries are often highly motivated believers that show higher rates of Bible reading, missional activity, prayer and giving than the rates he finds among church members for the same activities. (This matches similar findings in A Churchless Faith.) He believes that within a generation it is possible that only about one third of believers will be a part of anything resembling what we today call a church. It is not that folks won't be connected to "the Church," the just won't be "doing church" as we have done it because they will be to busy "being the Church."
I found a review of the book at Next-Wave that I thought was pretty good. I recommend the book.