That's still not a very good idea. Part of good sysadmin philosophy is to keep the OS itself as pure as possible and that means you do not replace tools that it comes with, including Perl. Why? Well, do you know what scripts came with the OS that use Perl? Do you know if swapping it out will break any of them? What about some 3rd party software that makes use of the Perl that comes with the OS? What about future patches, updates, and upgrades?
To be fair, this is probably not as obvious on Linux so let me give a better example: Solaris 8 comes with Perl 5.005_03. I think we can all agree that swapping this out for Perl 5.6.1 could be problematic and Perl 5.8.x would likely be even worse.
Short version is you should always install your own, separate Perl.