Mosman Ning is great. What i like about nings is that they can bring together a whole range of inforamtion and comunication applications within the one interface. The whole package would seem to me to be very attractive in developing a community of users with some common interest. I particularly like that it is easy for users to add content - this gives them a sense of ownership and belonging in the ning.

What i dont like is the cluttered nature of the example pages. Too many words - too many categories of items. Use more icons and limit them to 5-6 high value sections.
I also wonder about the amount of input required to maintain the content on these pages to the required standard and with a high level of content turnover. I guess the idea is that you develop a wider set of content providers and after a while they run themselves.