People have been calling these ‘gestures’. They are a facebook action which the developer defines in the new open graph. It is the equivalent of a ‘like’ action, but can be changed depending on the user action ->
https://developers.facebook.com/docs/beta/opengraph
It basically means dev’s can add verbs in to describe how a user is using the application.
These must be approved be facebook before they can go live, so obviously they cant be too crude…
They also require a user to accept permissions before they can initialize a posting to a wall.
It will need to be developed as a facebook app, but does not have to be embedded as a facebook app or tab (although the guardian one is).
So you would have to develop an app and integrate it with your website. Since you need to get user permissions (in the form of an access token) before you can use the open graph, you will need a call to action to get the user to get the user to allow posts. So you can’t just do this automatically. The plus side is, with the new Facebook rules (since they implemented OAuth 2.0 security), you only have to get permissions once, then the app can post on the user’s wall without asking permission to ‘share’ each time you post.
There’s no wp plugin, since you have to integrate an application via facebook…