There are two mailing lists maintained for the Theora project. This is the best place to ask questions, contact the developers or other users, or otherwise discuss the Theora video codec.
List
Archives for all Xiph.org projects including Theora
Subscription
information for all Xiph.org projects including Theora
There's also an active IRC channel for Theora.
Join #theora on irc.freenode.net.
You can also document concerns, applications, howto instructions, usage, support or anything else related to theora in the Xiph.org Wiki. We find this a good resource for documenting the outcomes of discussions and keeping track of various projects, and anyone can help edit the pages!
Should you encounter problems you can file a report over at the Xiph.org bug tracker.