$query = Array
(
    [status] => 1
    [uid] => 1
    [@fields] => Array
        (
            [$elemMatch] => Array
                (
                    [ex_node_group.value] => 4
                    [tag_summary.value] => Array
                        (
                            [$all] => Array
                                (
                                    [0] => 307
                                )

                        )

                )

        )

)
jsonp1271192441610({"total":0,"items":[]});

// Here's the mongo call:
  $rows = mongodb_collection('fields_current', 'node')->find($query, array('nid' => TRUE))->sort(array('created' => -1))->skip($offset)->limit($limit);
  $total = mongodb_collection('fields_current', 'node')->count($query);