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.