"Just" upgraded to Perl 5.6? "Just"? I don't think there has ever been a Perl releases that did not break scripts out there. Every Perl release breaks things. Sometimes intentional. Sometimes because of a bugfix. Sometimes because a feature is suddenly considered a bug, or bad coding style, and it gets "fixed". Sometimes because behaviour was unspecified (but consistent) and then it got specified to act different from how it always worked. And often the breakage was unintentional.

There are (very) large companies out there, with tens of thousands of users using hundreds or thousands of tools who might take a year to roll out a new version of Perl. And who *intentionally* do not upgrade because of the breakage.

One can't assume that what you can do on your home PC - just upgrading Perl in 20 minutes - one can do everywhere.