In a recent journal entry, brian d foy, seasoned Perl hacker and publisher of The Perl Review
, wrote about reducing the number of old distributions on CPAN to try to get it down to a level where it could fit on a cdrom.
The intention is not to delete modules: just old versions that are of no use except as an archive.
Even when these files are deleted from CPAN they will still be available on BackPAN so you can point users there if they need an older version.
You can see some interesting CPAN data at Perl at a glance. Brian refers to the effective size of CPAN as the Schwartz factor. Read his journal entry for more information. If you are a CPAN author you can clean up you directory here.