Allowing logged in users to comment without moderation across a multisite installation

You could hook into 'pre_comment_approved' and change its return value. Sample code, not tested:

add_filter( 'pre_comment_approved', 'wpse47172_approve_logged_in_users' );

function wpse47172_approve_logged_in_users( $approved )
{
    return is_user_logged_in() ? 1 : $approved;
}