What has always impressed me is the consistency and quality of the documentation of most CPAN modules. There's a huge group of people working at improving perl infrastructure and they don't get half the credit that they deserve!
Some examples:
http://search.cpan.org/dist/DBI/DBI.pm
http://search.cpan.org/~mlehmann/AnyEvent/lib/AnyEvent.pm
http://search.cpan.org/~melo/Redis/lib/Redis.pm
http://search.cpan.org/~abw/Template-Toolkit/
http://search.cpan.org/~ether/Moose/
It is just ridiculous. Searching around CPAN can become an odyssey.