/**
 * Return TRUE if the entity is acting as a group.
 *
 * @param $entity_type
 *   The entity type.
 * @param $entity
 *   The entity object, or the entity ID.
 */
function og_is_group($entity_type, $entity) {
  $wrapper = entity_metadata_wrapper($entity_type, $entity);
  $bundle = $wrapper->getBundle();

  if (!field_info_instance($entity_type, OG_GROUP_FIELD, $bundle)) {
    return variable_get("og_is_group__{$entity_type}__{$bundle}", FALSE);
  }
  return !empty($wrapper->{OG_GROUP_FIELD}) && $wrapper->{OG_GROUP_FIELD}->value();
}