Metrics
To help me keep track on the amount of plugin and version usage I use the Metrics tracking plugin. This plugin does not obtain any personal data, just wether you are using the plugin or not and of which version. If you do not wish to help and contribute you can disable this by going to your plugins folder and then find PluginMetrics/config.yml and set opt-out to true. All information collected can easily be reviewed at this page http:mcstats.org/.