Ooooohhhh... I like Ning and Gather. I liked that they are organized around interests and topics and that you don't have to sign up to see what is there. I joined both of them. I did a couple of searches and found some things I'm really interested in. I was already familiar with WebJunction having taken some of the offered courses. It's a really good way to get self-paced information on library topics of interest or that you need to help do your job better.
Fun with Shelfari. I added the widget to my blog.