ok, i've taken the plunge and decided to integrate my sites better with facebook.
first big glaring question though, i can add the open graph metatags to the head of one of my pages no problem...
however i notice on this page: https://developers.facebook.com/docs/opengraphprotocol/
they are adding an extra couple xml namespaces ... do i have to do this, and if i do, does this mean i'm going to have to convert my pages to xhtml, which i'd rather not as they are currently html5 and i'm happy with them.
You don't need to use xhtml to add opengraph metatags, you can add them to html5.
Your link is to an old version of the opengraph syntax. The old version didn't use xhtml either, they just used those namespace declarations as trigger text; and that trigger text is no longer required.
The Like Button page has a opengraph tags generator here (below the button generator): [developers.facebook.com...]