I have in the past taken a slightly entertaining approach and referred to user groups as Kind and Gentle People, Project Enthusiasts, Willing Participants, Avid Fans ... you get the idea.

In general, to counteract the impression of dehumanization so common in software, I recommend erring on the opposite side - create a unique voice and tone. Anything that breaks the monotony of reading endless lines of undifferentiated text, any phrases or words that will bring a smile to people's face, and anything that reminds folks that real people created this software for other actual humans is generally well received.