Search your homedir for a file called perllocal.pod. It lists all the packages you've installed. Assuming, of course, that your toolchain supports perllocal (cpan and cpanp both do, but I don't know about others).

The section for one installed module looks like...

=head2 Thu Feb 17 19:27:04 2011: C<Module> L<DBI|DBI>

=over 4

=item *

C<installed into: /usr/local/lib/perl5/site_perl/5.12.3>

=item *

C<LINKTYPE: dynamic>

=item *

C<VERSION: 1.616>

=item *

C<EXE_FILES: dbiproxy dbiprof dbilogstrip>

=back
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