I noticed that unknown variable messages have changed from E_WARNING to E_NOTICE.
With PHP Version 4.1.2 the follwing code gives a warning message that $foo is not known. I Upgraded to PHP 4.2.3 and now there is *no* message anymore :-(

<?
error_reporting(E_ALL);
class bla {
  var $foo;
  function bla() {
    echo $this->foo;
  }
}

$c = new bla();
// the follwoing line stille produces a message:
//echo $bar;

?>