At least with this article, it sounds like she really uses these services as opposed to someone that just heard about them and rags on it without ever really trying it out.
Online communities were never meant to supplant ones in your in-person life. It just adds another dimension to it. Sure, you'll get people that go overboard and cut off their in-person relationships, but they're the outliers. For certain types of interaction you'll probably find that most people would prefer face to face interactions. These types of interactions include friends that you already know and for finding mates. It's for that reason that friends still get together when they're in town and that people on match.com still meet first before committing.
For other types of interactions, like Brad Pitt fan club forums, World of warcraft (online game), and scientific google groups, your only interest in the other people is only within the confines of those contexts. And while that's what I imagine rubs people like the author of the NYTimes article the wrong way (having a cafeteria tray attitude to getting to know people). The people we interact with no longer has to fill every aspect of our social needs. It is acceptable now to have friends you only hang out with, friends you only tell secrets to, and friends you only go on naked streaking parties with. The same goes with people you interact with online.
Cars and suburbs have probably done more to keep people apart from each other than the internet has. Think about it. You use to have to walk to the local store, passing people in your neighborhood that you knew along the way. Now, you just drive on the highway. Suburbs rarely have sidewalks, and things are further apart, so people use their cars to drive, and not interact with each other.
And even if there were people around, you wouldn't necessarily want to talk to them. Out of all the times you've ridden the subway, when was the last time you struck up a conversation with a stranger sitting next to you? I'd venture to say, very few. Now if you lived on the West Coast (except LA)...maybe things would be different.
In addition, I've often discovered that some people didn't keep friends in a certain part of their life because, "We just hung out together, and did stuff. We didn't really get to know each other." Just because a relationship is face to face doesn't mean that you will have a deeper connection with each other. No matter what the medium, it takes effort on both sides. Besides, just because there are people around doesn't mean you're not lonely. I had always taken Nighthawks to illustrate that, and Edward Hopper was way before the internet.
Presence doesn't have to be physical anymore. It can be across different spaces, and even asynchronously across different times. While these forms of communications like cell, IM, email, blogs, wikis, forums, VoIP, etc are just facsimilies of face to face interactions, they're good enough for what we need to get done or enjoy just a snippet of each other. Between friends that can't meet face to face all the time, it's better than nothing.
And some forms of communication and interaction, while more limited to face to face, actually are beneficial in other ways. There'd be no way you'd be able to produce an encyclopedia from a room full of hundreds of people, as you do with Wikipedia. Online forums leave a trail of solutions to questions and problems others have encountered. I can't tell you how many times I've gotten help with configuring my linux box or rails when I've hit upon a wall from the dregs of people helping each other.
The current body of social network web applications, however, do have a problem. While novel at first, you quickly realize that they don't actually DO anything. If it helped people connect to not only their friends, but also connected you to like-minded strangers, or MOVED people to action, then that would really be something. But the current incarnation of social networks have much to be desired. Like all revolutions, it always takes a bit of tweaking, yet it's not going away. Developers are experimenting with other types of social networks, such as the recent Twttr and Dodgeball.
Online communications are here to stay, and like all things, it's good in moderation. No matter the medium, it takes effort and attention from both parties. It's the dual act of giving and receiving that makes a relationship between humans worthwhile. Online communications only provide the conduit, even if it's a facsimilie of real life. But it's up to you to do the rest and fill it up with meaningful content.