I had already joined Ning, but I posted a query and also did a search, joining Ning for the NLLN region of which I'm a part. One thing I've noticed is that most of the conversations happening on these library Nings revolve around Ning itself, rather than some separate library question or issue. It's akin to sitting in a car and debating the merits or drawbacks of the vehicle in question instead of actually going someplace.
I understand that Ning like many of the Web 2.0 social sites is quite new and there is bound to be discussion about it. I'm just hoping that the best sites will survive and we can move on to actually using them for professional communication and growth.