So I have to disagree with Michael Arrington when he says that Ning was “the perfect service at the perfect time“.
Social networking sites are powerful beasts, and clearly, they have the ability to get a lot of people connected, excited, and delirious enough to throw money at them.
But the ability to create your own social networking site? I just don’t think that is something that a lot of people can successfully do. They’ll dabble in it, they’ll play with it, yes, they may even create one for Nebraskan shark wrestlers, but it won’t be successful.
The problem is that the power of the social network is the number of people in the network. Social networks fail not because of the lack of some key feature but because they never get a critical mass of users so it can grow on its own. Despite the undeniable power of viral growth, viral growth actually rarely just works. Friendster, MySpace, etc. weren’t accidents. It needs the care and feeding of someone with a mind (and time and $) for PR, business development, and marketing.
Most people making mashups don’t have that. And Ning doesn’t help you.
Ramblings of a Short Man 
(Initial disclaimer: I work for Ning.)
All good points, with one notable exception: Ning is not, currently, a social networking site. We’ve had a couple of simple, small social networking apps, but primarily we’re a platform for creating new apps. However, you’re right in that it’s all about critical mass, and we’re not there yet. But this is not news to us, nor reason to write us off. We’re only a small way into our overall plan, much of which involves radically improving the ease-of-app-creation for non-technical users, out of which we hope to get more useful apps, out of which we hope to get more users. We are certainly putting work into PR, biz dev and marketing, though today has certainly been a wake-up call that we’re not doing enough.