I think as people start to have kids it would be less appealing, but people seem to be doing that later these days (or not at all).
According to the article the quality of the pool matters. If you want a neighborhood feel, the challenge is to come up with 8-40 people who are going to jive. Devon noted that (at least one) FoaF experience didn't work out. I think it is great if you have the social sense to select such a chill group but I'd be surprised if many people could accomplish organizing a successful large group.