This plugin is a plugin to aid management and uptodateness (if that's not a word it is now) of you plugins.
To use you must have it installed and you must select another user of this plugin whose uptodateness will serve as your benchmark.
In settings you will have a chance to nominate your benchmark blog by giving the blogs base install URL.
It requests a special page from the benchmark blog using a GET URL containing the version number, author, URL and plugin name of one plugin. The responding blog will then try to find the plugin and will tell you if it differs at all. If it has not got the plugin it will tell you the URL that it uses to validate.