The intermediate perl book recommends not setting PERL5LIB system wide for all users. Users who have discovered CPAN will mess around with that variable.

The book recommends adjusting the source and recompiling instead, which does sound like a load of pain to me.

Why not just put your modules in /usr/local/lib/site_perl? That should be in @INC.

EDIT: just checked, it's /usr/local/lib/perl5 on CentOS.