If you want to discuss dia, or problems you have with dia, there is a mailing list available. The mailing list address is:
dia-list@gnome.org
The reply-to header is set by the mailing list manager, so responses will be sent to the list, so you will have to be subscribed to get the answers to your questions. You can subscribe by filling out the form at the dia-list pages.
Archives of the mailing list are available at:
http://mail.gnome.org/archives/dia-list/
Older posts can be found at:
http://www.mail-archive.com/dia-list@lysator.liu.se/
Dia uses the the GNOME bug tracking system. You can either use bug-buddy to submit reports or follow the instructions at bugzilla.gnome.org. Use the package name dia when submitting bugs, and don't change the severity of your report unless you know what they mean.