This is a really neat idea! I didn't think of allowing the kids to backchannel and I'm not sure about it at my level - junior high - but it's something I, now, can think about and try to determine if there's a way to make it work.
Our SS students use glogster to create on-line projects with a variety of media (pictures, videos, sounds, voice threads etc). Our teachers have found that the students really enjoy it and that it is relatively easy to manage. We also use skype, google earth and twitter in the classrooms.
I haven't used Glogster, yet, but have explored it a bit. I do think it has some great possibilities in the SS classroom, especially, at the junior high level. Thank you for bringing it up and confirming that it is being used, currently, in SS.
I have used www.glogster.com I used this with the American Revolution unit. I had all the students pick a topic from a list created by myself to create a glog about the American Revolution in North Carolina. The students used all kinds of images, video, audio uploads to tell me the importance of the event, battle, person, document or place. I will be doing this again with the Civil War Unit and agian for the Post WWII era. I also use this web 2.0 activity for a reading class to help students visualize books. They must include charactors, plot, setting, theme, time period. The kids love chatting with each other after they view the work done by fello classmates. I use glogster as a plce to upload quizzes, links to great sites, and extra credit activities.
I am not a Social Studies educator but I would think that the use of Web 2.0 tools would be based on what one is attempting to accomplish. For example if one wants to create a collaborative graphic organizer to better understand historical information one might use a web 2.0 tool such as Bubbl.us. If one wants to create a quiz, one might use a tool such as Quizlet. If one wants to edit text collaboratively one my use Google Docs.