There was a time when I was writing a module for CPAN, and I decided to try to make it compatible with old versions of Perl. First, I installed many versions of Perl in my machine. Not too much trouble, except that the old makefiles didn't work right away my newer system! But with some hacking I got them to compile. Then, I started to get rid of the ours, three-arg opens, and such until perl stopped complaining.
in reply to The need and the price of running on old versions of Perl
What was the result? That my module, which worked perfectly well with the newer perls (5.6.1+), even after the changes for compatibility, somehow caused the old perls to segfault. That's one of those errors that's "not supposed to happen" when you are writing pure Perl! So, from that moment on, I don't give a damn about supporting ancient perl versions such as 5.004. I'm willing to work around the lack of recent features and syntactic sugar, but I'm not willing to work around the bugs.