You can find a confused 'pastoral' viewpoint on just what is the "mainline" referred to in some of George Barna's recent research here (look under 'Emergent Conversation with Mike Horton') @ www.timsuttle.blogspot.com
. However, you can see from this link (http://www.christianitytoday.com/ct/2006/007/21.56.html
) that the mainline referred to is in fact, the old, liberal protestant (and I use the latter label very loosely, since they don't protest anything, with the exception of orthodoxy) mainline denominations.
P.S. (to Tim) - FYI - Yer buddy Tom Oden is the author, not only of "Turning Around the Mainline," AND "The Rebirth of Orthodoxy," but also the general editor of The Ancient Christian Commentary on Scripture." Go figure, eh?
g & p,