Users who have not been assigned any Roles or Capabilities are called 'orphans'. When using the shared users table trick to link up multiple WordPress installations, users who register on one of your blogs, are not given any privileges on the other blogs in the network. WP-Orphanage is a plugin that automatically adopts your orphan users by promoting them to the role of your choosing. By default it is the same as the default role set in the WP Options.
The v1.1 update fixes a bug introduced in the option screen in v1.0.1 and is recommended for all users of this plugin.