This is a non-definitive list of all the active discussion lists around the OSGeo projects.
Collabnet uses ezmlm for mailing list management, so if you know a list address, then to subscribe to it, email [listname]-subscribe@[project_subdomain].osgeo.org
Main discuss list
Incubation Committee list
Unused lists / groups?
Conference organising lists - they are the collabnet defaults, and none of them seem to have traffic.
Fundraising mailing lists - they are the collabnet defaults, and none of them seem to have traffic.