Copy and pasted from PHP 5.3.0 Release Announcement.

The PHP development team is proud to announce the immediate release of PHP 5.3.0. This release is a major improvement in the 5.X series, which includes a large number of new features and bug fixes.

The key features of PHP 5.3.0 include:

This release also drops several extensions and unifies the usage of internal APIs. Users should be aware of the following known backwards compatibility breaks:

  • Parameter parsing API unification will cause some functions to behave more
    or less strict when it comes to type juggling
  • Removed the following extensions: ext/mhash (see ext/hash), ext/msql, ext/pspell (see ext/enchant), ext/sybase (see ext/sybase_ct)
  • Moved the following extensions to PECL: ext/ming, ext/fbsql, ext/ncurses, ext/fdf
  • Removed zend.ze1_compatibility_mode

For users upgrading from PHP 5.2 there is a migration guide available here, detailing the changes between those releases and PHP 5.3.0.

For a full list of changes in PHP 5.3.0, see the ChangeLog.