Examining
http://www.google.com/, they achieve their perfect Facebook
link and logo through 100% old fashioned HTML goodness without a drop of
OG.
http://en.wikipedia.org/wiki/O.G._Original_Gangster ☻
And OK, if OG is the way to go, then perhaps MediaWiki should stuff some
in for the user, just like it does already on every page with
<link rel="search" ... href="/opensearch_desc.php"
which contains
xmlns:moz=...mozilla.org/2006/browser...
I mean there are probably a few $wg variables from LocalSetting.php that
could be referenced when creating the OG <meta> stuff, without needing
to ask the user questions about his wiki when he first sets it up, nor
needing him to install an extension.
Like $wgLogo for starters.