Well, in my previous example of the Online Tools for Educators community group, I discussed how this resource was open for all parties involved, whether they had a login name or not. The login is FREE, so taking a few extra minutes to create an account is no big deal, plus, it allows you to interact with other educators -- they can search through profiles by keywords to network with you as well!
I use Verizon Thinkfinity's community tool when teaching my graduate level online course entitled Web-Based Multimedia Design for Educators. Thinkfinity allows you to create groups for free within the community, you just need to have a login in order to do so (again, it's free). There are a lot of benefits of using Thinkfinity in the class, because it is a free open resource for educators. One of the things I like most about using it for teaching purposes is that I can create a NEW group for every semester I teach the class, and I have the ability to determine the accessibility of the group. I always make my course groups PRIVATE so that my students feel as though they can share with one another and not have the rest of the world reading their materials. That said, I do encourage my students to post to OTHER groups that have been created by other teachers on Thinkfinity, for the purposes of networking with THEIR colleagues in the schools/districts they work in.
To introduce the group to my students, I send invitations via email to have the students join. Then, I send them an email that contains an attachment in PDF format so that they get some additional information about how the community works. When I create my introduction screencasts for the course, I create one to discuss the syllabus, and another to discuss the class platform (usually eCollege, developed by Pearson) or Wikispaces, which I stopped using because I heard it wasn't going to be a free resource anymore, and I like to model free resources. Finally, I encourage my students to ask me any additional questions they may have about using the Thinkfinity community group.
Please let me know if I should include any additional information for this task.