I have installed the plugin on WordPress MU (WordPress 3.2.1) + BuddyPress latest stable version, and causes single blogs pages and posts stopped working.
The error is:
PHP Fatal error: Call to undefined function get_post_thumbnail_id() in .../public_html/wp-content/plugins/social-graph-protocol/index.php on line 318
A workaround would be to check if the function exists
if (function_exists('get_post_thumbnail_id')) ...