i use old versions of Perl all the time (i.e. RHEL 4/Perl 5.8.5). Occasionally I run into a problem with modules, but for the most part it all still works great. In one case the computer can't be updated, but it's necessary to continue development on it. It's running an old bugzilla system... and I've looked into porting it to a newer machine, but because it's so old, it's looking to be painful.