You can create new Ning "networks", but you cannot search for existing networks. Apparently the search feature was taken away because it was "primarily being used by people moving from one illegal Ning Network to another." http://blog.ning.com/2009/11/redesigned-ning-com-is-now-live...
It also makes them a lot more private which is a pretty significant feature in today's social web. The question is how important is that, and to how many people? My bet is the number is growing fast.
This makes Ning networks a lot less valuable.