Is "I want to keep me up-to-date with the new features of Perl, or at least the ones I am interested in" a good answer to "why upgrade?"
I am not a fan of the gimme-the-latest-version line: I prefer stability and my OS of choice is Debian Linux in fact, so I agree with you on the overall. But if you want to test the newest features, having a brand new Perl 5.8.0 aside of your older installations is a good choice, isn't it?
# Another Perl edition of a song:
# The End, by The Beatles
$you->take($love) eq $you->made($love) ;