Big fan of the site. We live in a small development (<100 homes), and it adds to the neighborhood feel. Not used by the HOA, it is grassroots. Recently, NextDoor tried an experiment to allow interaction with 'nearby neighborhoods' that was a disaster, and they pulled it after a couple of days. I disliked it because the sense of neighborhood was lost. Don't know how they're going to monetize it so that it is long term viable.
