"Unitarianism" v. "unitarianism":
I agree with my American Creation coblogger Brad Hart's post on "unitarianism" as the descriptive religion of America's key Founders (it was the political theology of the American Founding). He is absolutely right that an "enlightened" preacher like Charles Chauncy, who was both a theological unitarian and a universalist, spoke more to America's key Founders than did Jonathan Edwards, the prototypical Calvinist orthodox Christian theologian of that era.
However I must caution Hart about using the capital "U" when he speaks of "Unitarianism." (I know spell check tells you to capitalize it.) When we call America's key Founders -- Washington, J. Adams, Jefferson, Madison, & Franklin -- "Unitarians" and capitalize the "U," invariably some critic will take that out of context and note these Founders weren't members of "Unitarian" Churches. Washington, Jefferson and Madison were all likely "unitarians" in their theology, but none was a member of a "Unitarian" Church; all were affiliated with the Anglican/Episcopal Church.
Even John Adams, who was a "Congregationalist," testified his own church preached "unitarianism" as of 1750 and that he was one since that time. But I don't believe they were an official "Unitarian" Church until the early 19th Century.
Gary North notes this difference between unitarianism and Unitarianism in his Ebook. They were "unitarians," not necessarily "Unitarians." Likewise what Dr. Gregg Frazer terms "theistic rationalism" has unitarianism as an element (along with theism, Arminianism, universalim, syncretism, and rationalism; and by the way, this system with those elements was likely to present itself under the auspices of "rational Christianity" or "unitarian Christianity"; indeed Charles Chauncy presented himself as a "Christian minister" in a Congregational Church). That might be one reason why "theistic rationalism" is preferable to "unitarianism." But I use both terms interchangeably and sometimes write to purposefully alert the audience that the two terms are interchangeable; at least they are not inconsistent with one another, similar to how one can be a "Calvinist" and an "orthodox Christian" at the same time. Or how one can be a "Thomist" and a "Roman Catholic."