Ohloh tracks open source projects that have public version control repositories. Currently more than 10,000 projects are listed of which more than 2,000 use Perl. They've scanned nearly 59,000,000 lines of Perl.
Ironically if it were not for the CPAN (surely one of the world's most valuable collections of free software) Perl would, I believe, be even better represented. As this graph shows Perl doesn't feature particularly strongly in Ohloh's commit stats. Projects written in languages that don't have the benefit of a dedicated archive like CPAN tend to be hosted on Sourceforge or Google Code which automatically gets them a public repository that Ohloh can scan. CPAN modules tend to live between the author's computer and the CPAN and remain largely invisible to the wider community.
If you're a CPAN author whose modules are not listed on Ohloh consider adding them. If your code is in a public repository list that too. Let's get a more accurate picture of how much code the CPAN represents.
Sceptics will note that Ohloh's LoC (Lines of Code) and comment ratio metrics are flawed, tending to favour verbose languages and (I think) ignoring embedded POD. My impression is that the Ohloh team are actively working to improve their metrics. If Perl is well represented they will have a greater incentive to get the metrics right for Perl.
Show the rest of the free software world just how much high quality code we're cranking out. Add your Perl project to Ohloh today.