I think a more interesting question is how can you legimitately measure the sum of hobbyist growth, industry growth, and dominance of various languages. I'd say you can't -- and you shouldn't.

If you are concerned, don't be. More languages in your toolkit is always a good thing and if something else comes along, lessened learned from Perl still apply. Ruby and Python really exude much of what made Perl popular. PHP, well, I don't care for that one as much -- but it's slowly realizing that it needs to change.