Yay, finally we released PHP 5.5, which is a new big release for PHP. In preparation for this I yesterday sent out a mail to the PHP core developers stating that the "PHP-5.3 BRANCH IS CLOSED NOW". After I saw this quoted on twitter and different websites I want to make a few things clear for users of PHP:
The mail is an information for core developer that all changes for 5.3 should go by the release master and our security group
We won't do normal bug fixes
we will continue doing security fixes for a year where needed
What this means for users of PHP is that they can continue using PHP 5.3 and when upgrades come they are very low risk of breaking anything (we always try not to break anything, but any person's bug might be another person's feature) so they should be applicable easily and applied fast. So when you are a happy PHP 5.3 user and don't want to touch too many things there is no immediateneed to upgrade to 5.4 or 5.5 - for a year.
So even when you don't have to migrate why should you migrate? - Besides the new features I see two major reasons:
Newer versions of PHP are generally more performant and efficient than older versions, meaning your users get faster response and you need less hosting/cloud resources to run your system.
You get all bug fixes
So when migrating where should you go to? PHP 5.4 or 5.5? - There the answer is, in my personal, quite easy: Go to 5.5! 5.5 will live longer than 5.4 so it is the more future save path, as we try hard to keep backwards compatibility migration should be fairly simple, etc. PHP 5.5 also mostly uses the same code as 5.4 with a few extra features. So for everything PHP 5.4 does PHP 5.5 does it as stable.
So go and fetch PHP 5.5, use for new projects and work on your migration from 5.3 but don't panic.