PHP has recently upgraded to a new version and I was how many of you dedicated server owners out there have decided to upgrade.
I'm running PHP 5.1.4 myself, there doesn't look to be any backward compatibility issues in PHP 4.4.2, just bugfixes mainly..
I use the latest versions to run a server from my PC for testing purposes with PHP 5.1.4 The bundle comes with a switch back to 4.4.2 for compatibility issues but it seems there is none, in fact PHP 5 handles the old php3 and phtml formats