Absolutely. It's been noted above already, but Perl 5 isn't going anywhere for a long time. I was lucky enough to start with Perl a few revisions into 5 (5.005... I think? I'm not a great Perl historian ;). I still recall a lot of "If you're using < 5, do this..." FAQ answers. And, those were around for years.

In terms of releases for particular operating systems, 5 will be the standard for a while. I'm lumping Win32 into that as well, since Activestate isn't usually bleeding edge with the version they package. They stay within the current stable release. And, most *nix distributions (particularly including the BSDs and commercial *nixen) will have 5 in the stable branch for a long time to come.

Given that 5.6 is still actively supported, even with the wide adoption of 5.8, it just bolsters the case for starting wit 5 even more.