I have really enjoyed using social networking websites with my students. I first started using 21 Classes and had a nice experience with it. It had some limitations, though. One thing was the difficulty to embed other things into the pages. I liked to have all students in one front page from where they could access each other's blogs and explore the features they were so used to in their out of class social networks.
Next, I discovered ning. This one I have been using till today and I am planning to continue using this year. Ning is social networking at its best. Its features include forums, chat, blogs, photos, videos, integration with twitter, and some more. It is worth exploring.
Just yesterday I found out about twiducate on twitter (actually I think I had seen it before, but just yesterday I decided to give it a try). It seems simpler than the other ones and a bit more complete than twitter for what I wanted. I will have a group of beginner students and I really did not want to use ning to avoid overwhelming them with so many features. I also did not want to use a blog because it would be very teacher centered. So twiducate seems like a tool that is not the complex and will allow all students to interact in one place.
I posted this screencast to give those who might want to use it an idea of how it works. I hope it is helpful.