Today the latest stable version of PHP was announced, PHP 5.3.0.
Go download and play with the new features available such as namespaces, LSB, anonymous functions and closures along with many more bug fixes, additions and improvements.
My favourite addition at the moment is the improvements made to the DateTime extension with new classes such as DatePeriod (for iterating over dates/times) and DateInterval and additions to the DateTime class such as DateTime::createFromFormat and DateTime::add (and sub).
The anonymous functions will also be very useful where one might previously use create_function (or a normal non-anonymous function) in particular for callbacks to other functions/methods.
<?php
echo preg_replace_callback('/[A-Z]/', function ($match) {
return str_rot13($match[0]);
}, 'Uello Jorld!');
?>
echo preg_replace_callback('/[A-Z]/', function ($match) {
return str_rot13($match[0]);
}, 'Uello Jorld!');
?>
So, download it and have an explore. 
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