Ning is an okay social network for teachers. Teachers are able to share resources and give ideas on lessons. I also noticed that you can join different specific groups to share lessons. What I do like is the Forums sections. Librarians post questions that where they need professional feedback about what is happening in their schools.
Here are a few forum questions:
But I like social networking for find friends from high school, previous co-workers, friends from CA, and friends from Guam. I also like Askville.com by Amazon. I can post a question and people of that network can answer and further ask questions. I posted this questions several months ago on grammar.