No personal data is stored by this plugin.
The plugin uses only one cookie (wp-gdrts-log) for non-logged in visitors to track votes. If you don’t allow votes for non-logged in visitors, this cookie will not be used.
The plugin is logging IP’s into votes log for each vote logged. IP’s are used to prevent the duplicated voting, and it can be used to geo-locate votes on administrator request.
But, if you don’t need the actual IP’s, but you still need to ability to prevent duplicated voting, GD Rating System can replace IP’s with hashed strings. This way, you don’t store actual IP’s, and hash strings can be used to prevent duplicated voting. More information on that is available here.