I was hesitant with NextDoor but I've found they do in fact provide very real value. At least for living in a city like San Francisco where you're not likely to actually know many of your neighbors.

My only concern is that it's starting to turn into a FUD (fear, uncertainty, and death) distribution machine. Pando Daily gave them a great review for keeping neighbors informed about crime[1]. However, now crime, muggings, etc are most of what I see on the site. Has my neighborhood suddenly become significantly less safe? Why don't I actually see this increase anywhere around me? Am I just that unaware or is this just a lot of noise? I don't actually have an answer, but it raises the question: is this actually good for me to consume or is this just the go to place to be afraid of your neighborhood?

That said, I've gotten great advice on where to find live dungeness crab in the city through the site.

[1] http://pandodaily.com/2013/01/22/nextdoors-unexpected-killer...