As a historian of religion looking at the congregrations I have attended, I have to smile. Because they do have a creed, and they do have a belief system that holds them together, although this does not appear to me to be a common theology.
As for the creed and the belief system, it is embodied in their value system, seven values that they hold in common. These values under gird the UU congregrations. It is what holds the religion together, and it is what is so exciting about the tradition. Here is a group of people who are inclusive, having major religious differences, and yet remain as a community because of their core values. What I miss in UU congregrations is the continuity of story and liturgy, although I find it refreshing that each and every person is supported in his or her own personal spiritual journey.