I joined the Ning in Round 2, since I did not participate in Round 1. I didn't find an appropriate group to join, so I created a group for MLIS students. So far, I am the only member. I am not sure if any of my St. Kate's classmates are participating in the Things.
I can only speak hypothetically of how I would use Ning in "my" library, since I don't yet have one. But I can see it being a useful tool in a branch library or a school library as an informal way to converse with patrons/students about things happening in the library. I have used Ning to keep intouch with relatives. We would share pics and reminiscences about loved ones who have passed on. But after a brief spurt of activity, we all started to communicate on facebook instead. I do like having the opportunity to email my photos in so I don't have to sit there waiting for them to upload.
I did enjoy seeing other people's photos of their libraries. Some of them were very nicely laid out and inviting!