The PHP 5.3.3 was released a few days ago.
The PHP core team has announced the 5.3.3 availability. This release has focused on improve security and stability issues with more than 100 fixed bugs, most of them related to security issues.
Previous versions incompatibility
For previous version than 5.3.3 there is a big incompatibility. The methods with the same name as the class name used by the namespace are not anymore considered as the class constructor. This change does not affect the classes those do not use namespaces.
public function Bar()
// Act as constructor in PHP 5.3.0-5.3.2
// Act as a regular method in PHP 5.3.3
This change does not have impact in migrations from PHP 5.2.x, due to namespaces were introduced from PHP 5.3.0.