The following code demonstrates the 'feature' ...

<CODE>
function myfunc(&$value, $key, &$user) {
	$value = "$user:$value";
	$user++;
	printf("%3d : %s\n", $key, $value);
}

$myarray=array("one", "two", "three");
$myvar=1;
array_walk($myarray, "myfunc", $myvar);
echo "myvar=$myvar";
</CODE>

This code outputs the following ...

<SAMP>
  0 : 1:one
  1 : 2:two
  2 : 3:three
myvar=1
</SAMP>

myvar has been incremented between calls within array_walk but the final
value is not passed back to the original variable.

I understand that the above usage is not mentioned in the docs but it would
be a nice feature to have.  The current functionality seems to be somewhat
inconsistent and I doubt its usefulness.