One of the down sides of services like Ning is that your social network is resident on the same domain as everyone elses social network. This probably is not good from a search engine point of view, unless google et al have programed their software to make allowances for Ning, as they probably do for Facebook. I have never used Ning and so I am not sure about the bespoke customisation aspects of Ning but I imagine you will never be in complete control of 'all' aspects of your social network code. see more Media server aspects of Ning I am also unsure of.