not compatible with good old software...legacy hardware
++ for bringing that up. And hardware doesn't just mean CPU and HDD and RAM -- it can be other proprietary hardware connected-to-and-run-by the good old software. So "update OS" or "update perl" isn't always an option. (That's has been one of my situations at $work.)
maintain legacy compatibility of retro systems
On the other hand, I disagree with this. The developers of perl and developers of CPAN modules shouldn't be beholden to those of us with legacy needs. Perl makes available old copies of the language, so that's not a problem. CPAN keeps old versions of modules, which you can download (the common CPAN clients even allow you choosing version and/or URL for a given module's distro) ... and even if the author has deleted ancient versions of their modules from active CPAN, it's still on the BackPAN. So if you have a set of perl-version-plus-modules that worked a decade ago, that same set of perl-version-plus-modules is still available to you.
