There are a number of flavors of unitarianism; UU is perhaps the most well-known, not to mention the most detached from being in point of fact truly unitarian in its theology.
One popular breed of modern theological unitarianism is oneness pentecostalism, as exemplified by denominations like the UPCI (http://www.upci.org/). These churches assert that father, son, and holy spirit are in fact three offices ("modes") of a truly and totally singular unipersonal god ("monad"); their position is more formally known as modalistic monarchianism.
Other curious properties of this sect:
- They interpret 1 Corinthians 11 to mean that women should not cut their hair, ever, period. This interpretation quite exceeds the literal reading of the text.
- There is a tendancy towards using the KJV translation exclusively, giving it preference over even the hebrew and greek texts from which it was derived.
- Members of this sect tend to refer to themselves as "apostolic" as they believe their doctrine to be that of the original apostles; this is not to be mistaken with the ministry of modern apostles or references to the "New Apostolic Reformation" which are trinitarian movements.
- It strikes me as odd that this doctrine is present in a pentecostal movement with a strong emphasis upon the Holy Spirit as such.