Perhaps more important, Nextdoor is private: Only verified neighbors can see each other's posts, and Nextdoor neighborhoods' pages are not indexed on any search engines. Some other community sites allow anonymity, which has encouraged incidents of nasty small-town gossip. (See this New York Times story about a site called Topix, on which rural users anonymously slag each other—e.g. "Has anyone noticed she is shaped like a penguin.") Tolia says that using real names and addresses has kept Nextdoor free of vicious name-calling and rumor-spreading. The Nextdoor users I spoke to agreed that this is the case.
To me, the more relevant question is whether we need, or want, to have any connection at all with the random grab-bag of strangers who happen to live nearby. We can sell stuff on Craigslist, give it away on Freecycle, find recommendations on Yelp. Is there something special about doing this stuff within a tightly knit, exclusive circle of neighbors—establishing a bond based on proximity?
I live in a 75-unit apartment building. I know only two of my neighbors by name. The woman across the hall (who once invited me over for a delicious Rosh Hashanah dinner) seems like a lovely person, and she returned my folding chairs promptly after she borrowed them. But then there's this other dude.
This guy—let's call him Larry—managed to invite himself into my apartment shortly after I moved in, when I was surrounded by open boxes and crumpled packing tape. Within minutes, he'd begun bragging to me about how he cheats on his wife. Since then, he has knocked on my door and 1) asked if I wanted to buy some cocaine, 2) insisted that he wanted to hire a prostitute for me—his treat, and 3) suggested we film some porn in my apartment, with him behind the camera and me as the star. I declined these offers.
Yes, I should have drawn firmer boundaries with Larry. Maybe right after that first visit. But I'm a nice guy, I didn't want to offend him, and it seemed much easier to nod and smile until he went away. Besides, and this is the key: He knew where I lived, and I had no choice but to see him all the time. Telling him off might result in a lot of very awkward moments in the elevator or the mailroom. Didn't seem worth it. I just waited for him to move out. Which he finally did, to my tremendous relief.
It's people like Larry that make us crave anonymity within our neighborhoods. Once even a shred of a relationship has been established, a neighbor might pound on your door at any moment, sidle up to you while you're jogging, or maneuver next to you in line at the corner store. We can't block them, as we can with annoying people on Facebook. The real life equivalent of blocking is a restraining order. That seems a bit messy and is likely overkill in a situation like this.
But while we may not want to be friends with our neighbors, there are still reasons to be neighborly. Moments of sudden need, a la the aforementioned folding chair borrowing. (Nextdoor wants to establish "lending libraries" so neighbors can arrange to share leafblowers and extension ladders and such.) Safety concerns. (There's some evidence that Neighborhood Watch is an effective program, and Tolia gets excited when he discusses the potential for Nextdoor to reduce crime rates.) Raising awareness around community issues. (There have been attempts to integrate local governments into Nextdoor sites—with posting but not viewing privileges, so they can broadcast information and alerts without spying on their citizens.)
All in all, it seems like Nextdoor may offer most of the benefits of neighborliness with few of the icky downsides. You can establish online ties with your neighbors, thereby eliminating the need to ever interact with them in person. Or—in a best-case scenario—the online connection might manage to surface some cool nearby folks you actually do want to have a beer with. I'm thinking I might go ahead and start a Nextdoor site for my building. Once I'm completely certain that Larry's gone.