Just a heads up- with version 1.5.4 of the mongo extension, next() is not returning the same result as its alias getNext() (http://php.net/manual/en/mongocursor.getnext.php). An array is returned with null values.
(PECL mongo >=0.9.0)
MongoCursor::next — Advances the cursor to the next result
This function has no parameters.