I think Ning may be falling into a common trap. Just like many websites obsess over their visitor numbers, Ning obsesses over the number of networks created. This affects the site design: right on the front page, there's a huge "Create" widget that doesn't even check if something with the same name already exists. Try doing a search for say, "entrepreneurs." You'll get dozens of little networks, many of which have identical goals.

This duplication clearly hurts Ning: because of the network effect, merging two networks doesn't make it twice as useful -- it makes it four times as useful. I'm sure Ning knows this, but they aren't able to do anything about it because if they change the design, and the pace of network creation slows down, their investors might look at the chart and panic.

Ning is unique in their space, so right now they don't have much to worry about. But they have to be really careful about the fragmentation or else at some point they will have more networks than users and the useful activity will get drowned out in a sea of noise.