I am leaning to agree with Peter on this one... I don't think we need a flex-users list until we have an Apache Flex release.
Any discussion on Flex Best Practices, at this moment in time, would be exclusively based on Adobe Flex, for which there already exists a best practices document (which nobody follows), I believe it's at http://opensource.adobe.com, but I could be wrong because I don't really follow it... ;) -omar