The README in /Library/Perl/Updates
In the module search order (@INC), this directory comes before the system
perl directory, so modules installed here can be used to update perl-standard
modules. The installprivlib Config parameter is now set to this directory,
so that (for instance) setting INSTALLDIRS=perl will cause modules to be
So it sounds like if you've got modules that are acting up in there, you should be able to clear this directory out to get back to normal (as in, nothing new's installed).
What I'd really suggest is installing MacPorts (http://macports.org) and building your own Perl 5.10. It's always dicey to mess with the system Perl, as anything in the system that depends on it will also get broken if you break the system Perl.