В новом релизе PHP 5.1 были обнаружены серьёзные ошибки, поэтому всем рекомендуют обновиться.
* Native date class is withdrawn to prevent namespace conflict with PEAR's date package.
* Fixed fatal parse error when the last line of the script is a PHP comment.
* eval() hangs when the code being evaluated ends with a comment.
* Usage of \{$var} in PHP 5.1.0 resulted in the output of {$var} instead of the $var variable's value enclosed in {}.
* Fixed inconsistency in the format of PHP_AUTH_DIGEST between Apache 1 and 2 sapis.
* Improved safe_mode/open_basedir checks inside the cURL extension.
Changelog: http://www.php.net/ChangeLog-5.php#5.1.1
>>> Подробности
