> Has anyone been to a Unitarian Universalist service?
I have; 30 - 40 times a year for 30 years. Many of them are laid out like a liberal protesant service; hyms, readings and a sermon. The sermon topics are more wide-ranging, though.
Our congregation has had non-typical services; a lesson in pagan dancing, and all-joke service, lectures by a philosopher on the ethics of genetic research, another by a rocket scientist and a third by a fellow who helped develop the GPS system. Every two or three years we have a "blessing of the animals", where children bring their pets and we meet on the lawn instead of inside.
"What do you do?" is so frequently asked that our congregation has a point-by-point order of service for the curious:
http://www.stanuu.org/oofs.html
No snake handling, no dancing naked by the light of the moon, no 90-minute lectures.
"What do they talk about?" is so frequently asked that our congregation's has a list of 8 sermon topics to give people an idea:
http://www.stanuu.org/services.html
It also has about 40 complete sermons, given by our minister
and by guests. Look for "Sermons" on the navigation bar if you are interested.
> are they usually active in their communities?
Yes, but not always as UUs. Ours, for instance, has members who are active in the local chapters of the ACLU, Sierra Club, NOW, the Memorial Society, an adult education program for seniors at the Community College, Amnesty International and the League of Women Voters. Other things too; those are the ones I know of, who talk about it.
As a congregation we send a team to Habitat for Humanity, and we feed 100 homeless people once a month.
The congregation near you may vary. Look at their web site. It will probably be better designed and prettier than ours, with less wry humor.