I think part of the perception that people can "believe whatever" is a misunderstanding. A key tenet of our Unitarian Universalist religious faith call on us to respect others, including those who believe things that are not necessarily consistent with our own faith. That tenet, for example, is not something that UUs can legitimately "not believe". It is something that calls on us UUs to welcome folks of other faiths into our church communities, and so it is true that many folks who aren't necessarily UU can still find a spiritual home at a UU church.
Please keep in mind that, while regular participation in Sunday services is ideal, there are many ways to engage a UU church community. For starters, our church offer Wednesday night services four times a year. Also, our church has a thriving small group ministry program that meets twice each month. It is intended as supplemental to Sunday services, but is part of the UU experience nonetheless and for some folks it is their own option given their Sunday morning commitments.
In addition, there are members of my church who you'll never see except at social action events such as beach clean-ups, the AIDS walk, or lobbying at the state house. And still others who, as alluded to above, are actually practicing a different religion in the abode provided for it within our UU church, and so they attend the regular services of that other religious faith which are held at other times during the week.
Finally, there is the Church of the Larger Fellowship, an online UU ministry. They have service Sunday evenings and Monday afternoons.
