Okay, everyone, help me out here!
Not having studied Unitarianism as closely as I have the Bah�'� Faith, I can't give the best of comparisons, but I can list a few aspects of the latter which I did not find in local UU congregations (since I have experience of only 3 or 4, I'm limited).
* Both communities of believers are very accepting everyone, from whatever religious background, but Bah�'�s convert (for want of a better word) to a unified theology. Such uniformity did not seem to be required of UU congregations. One Unitarian friend told me that he was free to believe whatever he wanted to, God or no God even, as long as he didn't try to make others do things his way. I don't know if this is part of UU theology or just his own.
* Believers in Bah�'u'll�h are subject to a set of laws governing both material and spiritual aspects of life. Everything from private personal prayer and meditation to marriage, burial, and service to the faith community and the world at large. These laws are universally applied--that is, every believer is bound by them, no matter to what local community they belong, or in what country they live. See this article:
http://www.bellaonline.com/articles/art33173.asp* The Bah�'� Faith is not a collection of independent congregations, loosely networked under the same name. Every believer is a member of the worldwide Bah�'� family. Administratively, the Bah�'� Faith is one unified whole, planet-wide, with its world headquarters on Mount Carmel, Haifa, Israel. See this article:
http://www.bellaonline.com/articles/art63322.asp* The religious literature of the Faith, its sacred texts, are separate and independent of Christianity, Islam, Judaism, etc. This is an independent religion, not a sect of Islam, for instance; and its followers believe it is the divine guidance for this time in history--neither the first nor the last chapter in God's ongoing religious guidance for mankind. That guidance has been going on since the beginning that has no beginning and will continue until the end that has no end. See this article:
http://www.bellaonline.com/articles/art26859.aspFor me, the main difference I found between the two was that the Bah�'� Faith offered a sense of universal cohesion, the commitment to predictable and universal set of laws, behaviors, goals and attitudes. There is an agreeable sense that we were all in it together, not competing, but combining forces to improve ourselves and the world around us. I wanted something that allowed for the heart's mysticism, without resulting in the superstition which comes of shutting down the logical mind. I wanted some unity, but without the either rigidity of fundamentalism, or the inefficient liberty of rugged individualism.
I wanted to change the world. The Bah�'� Faith holds the best promise.