We keep our files in Fluid's subversion repository: http://source.fluidproject.org/svn/design/engage
If you're new to using subversion, see: Subversion for Fluid designers using Versions
Current and past iterations of design activities can be found in our JIRA.
Design communication is done over the fluid-work mailing list. Meetings about specific design issues are announced over the list and added to the Fluid calendar.
Participation by everyone in our design communications over the list and in our meetings is welcome and encouraged!
More general information...