This can be enabled in permissions settings. A non-admin user who creates a project is automatically added as a project member (the first role is given, TODO: make this given role configurable).
Projects can be added from the public projects list.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2750 e93f8b46-1217-0410-a6f0-8f06a7374b81