The moment is there. PHP 5.4 was released in 2012 and has slowly become the industry standard. In August 2015, we will enforce this new standard to our users by completely dropping support for PHP 5.3. Please upgrade and enjoy the benefits!
O no, not another upgrade
If you feel like the title above ("O no, not another upgrade"), then there is something completely wrong with the way you maintain your hosting. Webapplications like Joomla and Magento continuously evolve and release updates (well, ok, some webapplications not as frequent as others). Extension updates (like for our own extensions) are released even quicker. And most site owners quickly install all these updates, hopefully after some testing.
But somehow, the PHP environment is often not upgraded that quickly. Most of the times, the PHP environment is also maintained by someone else - the hosting provider. And if the hosting provider is not eager to spend time on PHP upgrades that don't earn any extra money, the PHP environment simply remains on the same version for months, even years. This is wrong: PHP evolves, there are security fixes to implement, performance enhancements to be made. Not upgrading PHP means that you are choosing retarded backward compatibility, instead of running a modern environment. Upgrading PHP is vital.
So, PHP 5.4
PHP 5.3 is outdated and PHP 5.4 is current. Actually, it's not really true, because PHP 5.5 and PHP 5.6 have been there already for some time. Personally, we run all our development environments (with Joomla, Magento and custom code) on PHP 5.6 just fine. However, there are still some compatibility issues with PHP 5.6 (Magento its usage of Zend Framework 1 for instance), so running PHP 5.4 or 5.5 should give you the most stable experience.
I guess the biggest benefit of using PHP 5.4 is speed. The PHP project nowaways focuses a lot on making PHP perform better, and with every major release of PHP (5.4, 5.5, 5.6), speed is increased drastically. When you are running Joomla, you might consider PHP performance less of an issue, but with Magento, you definitely benefit from a simple PHP upgrade. If you are die-hard PHP dev, running HHVM is perhaps also an option. If you are not up to HHVM, at least run the latest PHP version possible.
Crossing over with development
Besides the benefits of PHP 5.4 that are in it for you - security and performance - there are also various things we are eager to implement. PHP 5.4 comes with various new features, among which traits. Traits are a new feature for PHP object-oriented programming and they allow for a class to inherit methods from multiple other classes. Thanks to traits, it is possible to spread out code more logically across multiple classes, making it easier to maintain and test, which again results in less bugs. We are eager to implement traits in some of our core libraries, libraries that are used in many of our extensions. By dropping PHP 5.3 support, we are able to jump forward and make this code improvement.
The date is set: 1st of August 2015
So the date is set: On the first of August 2015, we will drop all PHP 5.3 support. Currently, all our extensions and other software already supports PHP 5.4 till PHP 5.6 without issues. However, starting from August, we will make code enhancements that will causes crashes under PHP 5.3. This is not dramatic if you have a good hosting environment or simply keep your own servers updated. If you are still maintaining an old PHP environment, our advice is to stop modifying your applications and save up time and money to upgrade your environment instead.