If you could have a User Group for a file format, Open Document Fellowship would be that. Their mission is “To support the work of community volunteers in promoting, improving and providing user assistance for the OASIS Open Document Format for Office Applications (OpenDocument) and software designed to operate on data in this format.”
<p>This might even be enough to make The-Blogger-Formerly-Known-As-Ted-Roche to come out of retirement.</p>