Mailing list
We have a mailing list for pgSphere users and developers at Google Groups. You can read the mailing list archive on-line, but you need to become a member of the mailing list if you want to post messages.

To join the mailing list, write an e-mail message (subject line and contents do not matter) to pgsphere+subscribe@googlegroups.com. Shortly after that, you will get an e-mail message such as "Join request for pgSphere users and developers ...". Just reply to that e-mail without adding anything. That should be all. (Generally, do not use the URL provided in this "join request" message, as it will only work if you are currently logged into a Google account.)

Bug reports / issues
We use Github for bug and issue tracking. Go to https://github.com/pgsphere/pgsphere/issues to add a new issue (you can create a Github account in the process) or to browse old ones.
Wiki
The pgSphere wiki pages are at https://github.com/pgsphere/pgsphere/wiki. Anybody with a Github account is able to add to the wiki.