What are group homes like?

When I was volunteering to drive a church van, I picked up several people who lived in group homes. I have also known a few disabled people who live independently in their own apartments, and shun the idea of living in a group home.

So, what are they all about? Are they fairly supportive or are they just barely tolerable places to live? How are they certified? What is the overall atmosphere or gestalt or ambience like?