Right now, I'm not liking the PHP driver for MongoDB. Take a look at this example from http://www.php.net/manual/en/mongo.updates.php:

<?php/** suppose documents look like:
 * {"username" : "...", "password" : "...", "email" : "..."}
 */
$coll-> update(array("username" => "joe"), array("userId" => 12345, 
"info" => array("name" => "joe", "twitter" => "@joe4153", "email" => "..."),
"likes" => array()));

array(" I " => "want my JavaScript back")