While the United Church of Christ has had openly LGBT people in ordained ministry for decades, when the General Synod passed a resolution supporting equal marriage, many of our hold-out conservative churches and members left (about 250 or so, I think, of our then 5,500 congregations, including many more Puerto Rican congregations) so that we went from 1.5 million members to about 1.1 million.
However, we’ve since gained many members and many of our congregations that had previously been dying have been rejuvenated. Shodan is right, however, the number of conservatives who left and went to other denominations have greatly outnumbered, so far, the number of LGBT people and more-progressive thinking straight folks, particularly nationally-speaking.
Regionally, however, many of conferences have grown. The Northern California/Nevada Conference has grown substantially and many new congregations, particularly Asian-American churches, have joined since. I know that the South Central Conference pretty much doubled in size after the Cathedral of Hope in Dallas, Texas, (which self-identifies as the “world’s largest LGBT liberal church”) joined.
If the ELCA does indeed allow for the ordination of LGBT clergy, it will certainly result in many churches leaving and perhaps the formation of a new denomination. Both the LCMS and the WELS are very, very conservative, and I don’t know how many previously ELCA congregants that disagree with the ordination of gays and lesbians would still feel comfortable in either denomination. For one thing, the ordination of women within the ELCA is pretty much noncontroversial now; it is definitely not okay with either the LCMS or WELS.
However, it will be, in my opinion, a moral victory and a victory for the future of the church. GLBT people already contribute plenty to the church (this cite shows that there are plenty of gay Christians out there, and they are even “churchier” than straight people), and it’s about time mainline denominations figured out the just thing to do and acknowledge everyone who serves their congregations with passion and dedication.