I can see the path by which they grew out of traditional Christianity, but in their present form, the Unitarian Universalists seem to be an interfaith organization rather than a genuine branch of Christianity. (I'll note that there are Christians who are Unitarian in belief, and Christians who are Universalist in belief -- with apologies to CF's rules! -- but the UU as an organization has moved in an interfaith direction.)
They're friendly neighbors, though. When I'm doing social justice work, I can usually count on the UU churches to be there with us.
On the whole, I like their ethical values, and I like their commitment to intellectual exploration of religion; but for myself, I prefer to stay closer to the Nicene Creed.