PHP: What causes usort() to turn array into 1?

Can't get why usort() turns array into 1

Here is code of my sorting callback method in SomeClass

protected $_sortKey = '';

public function setSortKey($keyname)
{
    $this->_sortKey = $keyname;
}

public function sortByKeyValue($a, $b)
{
  $key = $this->_sortKey;

  if ($a->$key == $b->$key) {
   return 0;
  }
  return ($a->$key < $b->$key) ? -1 : 1;
}

Here is code where sorting takes place

$someObj = new SomeClass();
$someObj->setSortKey('name');

$sorted_stuff = usort($stuff_to_sort, array($someObj, 'sortByKeyValue'));

where $stuff_to_sort is:

Array
(
    [0] => stdClass Object
        (
            [id] => 57
            [status] => ACTIVE
            [updated] => 2010-09-17T12:16:25Z
            [name] => Windows Server 2008 SP2 x64 - MSSQL2K8R2
        )

    [1] => stdClass Object
        (
            [id] => 62
            [status] => ACTIVE
            [updated] => 2010-10-19T17:16:55Z
            [name] => Red Hat Enterprise Linux 5.5
        )

)

and $sorted_stuff gets value 1 instead of sorted array. What is wrong ?

PHP 5.2.17

see http://docs.php.net/function.usort:

bool usort ( array &$array , callback $cmp_function )

The sorted array is not the return value. usort() alters the array you're passing as the first argument.