At American Creation Eric Alan Isaacson writes of his recent "Unitarian Vacation" in Boston. It's notable how many of America's famous Founding era churches now belong to the Unitarian Universalists. Some highlights from his post:
Governor [John] Winthrop’s statue stands today outside his First Church’s current structure, which today accommodates the merged congregations of the First and Second Churches in Boston – the Second or “North” Church being a 1649 offshoot of First Church, where the Rev. Increase Mather and Cotton Mather held the pulpit in its early days, and where the Rev. Ralph Waldo Emerson would preach, from 1829 to 1832.
I suspect that Emerson would be gratified to know that the church’s office today features a portrait of his predecessor in the pulpit, the Puritan Rev. Increase Mather, on one wall, contemplating a statue of the Buddha standing against the far wall.
When we joined the Salem congregation for Sunday worship services on August 17, 2008, the Reverend Jeffrey Barz-Snell ceded his pulpit to a member of the congregation, Dr. Rose Wolf. Dr. Wolf identified herself as “a Christian witch,” and delivered a sermon on the subject of “The Emerald Tablet and the Golden Key: Reclaiming Jesus as a Witch.”
Our friend Tom Van Dyke, no fan of present day Unitarian Universalism commented:
What it said is that Unitarian Universalism has the physical possession of a number of Founding-era churches. However, that fact doesn't give Unitarian Universalism any theological claim to the "congregations" of that day or to the consciences of the Founders.
To conscript John Adams into Unitarian Universalism's positions on contemporary social issues falls short of intellectual honesty or credibility. Nor could we assert with any confidence whatsoever that John Adams would have been cool with a self-proclaimed witch in his pulpit.
This relates to an interesting dynamic: "unitarianism" and "universalism" were alive and well among the key Founding Fathers and the theologians they followed. Indeed, certainly Jefferson, J. Adams, and Franklin and likely Washington, Madison and many others were both unitarian and universalist in their theology. But if we say "did you know these Founders were unitarian-universalists?" that might intimate that they were like today's UUs when, in reality, they were different creatures. Theological unitarianism simply means the belief that Jesus is not fully God or the second person in a Triune Godhead. And theological universalism means the notion that all men will eventually be saved; most in the Founding era believed in a period of temporary punishment for the unsaved, eventual redemption. And indeed though many "key" Founders were attracted to unitarianism and universalism because they found these ideas "reasonable," some theologians argued for these positions from the Bible alone as the ultimate authority.
For instance, Charles Chauncy, who by the way presented these heterodox ideas under the auspices of "Christianity." As Nathan Hatch explained:
Charles Chauncy, pastor of Boston’s First Church for sixty years (1727-1787), is the most prominent example of an exclusive appeal to Biblical authority in order to unravel theological orthodoxy. Chauncy was persuaded to emphasize Bible study by reading the works of English divines, such as Samuel Clarke’s The Scripture-Doctrine of the Trinity (London, 1712) and John Taylor’s The Scripture-Doctrine of Original Sin (London, 1740). Both authors used a “free, impartial and diligent” method of examining Scripture to JETTISON, respectively, the doctrines of the Trinity and of Original Sin. 
During the 1750s, after the Great Awakening, Charles Chauncy spent seven years engaged in the approach to Bible study expounded by these English authors. In the spring of 1754 he wrote to a friend,
“I have made the Scriptures my sole study for about two years; and I think I have attained to a clearer understanding of them than I ever had before.”
His studies led him to draft a lengthy manuscript in which he REJECTED the idea of eternal punishment and embraced universalism. He kept this work in his desk for over a quarter-century, its conclusions, he confessed, too controversial “to admit of publication in this country.” He was nearly eighty when he finally allowed a London publisher in 1784 to print The Mystery Hid from Ages and Generations…or, the Salvation of All Men. To justify his conclusions, Chauncy relied on the biblical force of his argument, “a long and diligent comparing of Scripture with Scripture.” He explained to Ezra Stiles, “The whole is written from the Scripture account of the thing and not from any human scheme.” This unorthodox biblicist would have been gratified indeed by the reaction of one minister who, finding the book’s arguments convincing, wrote,
“He has placed many texts and passages of Scripture in a light altogether new to me, and I cannot help thinking his system not only rational, but Scriptural.” 
This is what the unitarian-universalism of the Founding era more looked like. But the problem of terming it "UU" and the confusion with contemporary UU still remains. But then what do we call it? Do we call it "Christianity"? Some will balk that like Mormonism it isn't "Christianity" whatever it calls itself. This is why Dr. Gregg Frazer has coined a new term to describe this system in which America's key Founders believed: "theistic rationalism."