There are actually quite a few subgroups on Dkos: the Food Group, the Energy Group (EnergizeAmerica), the edku group, TCers, PrettyBirdWomanHouse, etc. We usually set up on Google groups, or some like area. A lot of times it is just used to call the attention of group members to diaries or other articles/blogs/whatever that would be of interest to group members. Sometimes, like PrettyBirdWomanHouse, the group organizes actions to suppport the cause or, like the Food Group and EnergizeAmerica, organizes a panel for Netroots Nation.

While the information is more special-interest-specific, it isn't an "echo chamber" per se, since all of these are likely to have a lot of different viewpoints, even on a topic of common interest.