Adds personalised Open Graph tags that Facebook proposed, and constantly change their mind about supporting.
This program is part of the Pure Web Brilliant family, and requires the parent framework to be installed and activated. You can find that at: http://wordpress.org/extend/plugins/kevinjohn-gallagher-pure-web-brilliants-base-framework/
This plugin is an extension for the Pure Web Brilliant: Social Graph control plugin. It can be found at http://wordpress.org/extend/plugins/kevinjohn-gallagher-pure-web-brilliants-social-graph-control/
I don't know. They 100% do no harm, and they allow your website to have its information presented and searchable in a meaningful and semantic way. I personally use them on my sites.