I have looked at the Perl in PostgreSQL and it works fine. I have not used it in production only because I didn't have a need for those type of imbedded procedures. Where it would be useful would be where you wanted to work with some data as a procedure within the database so that whatever its triggered it the code gets run. Where I see perl excelling is in reformatting some text, or do something which plays to perl's strengths.
One Pg/SQL example I saw was changing some text, 'CONFIDENTIAL', into 'C O N F I D E N T I A L' and it was pretty cumbersome in Pg/SQL compared to a 1 liner in the embedded Perl so that's the type of place I see for the Perl interpreter inside PostgreSQL.
#basically this type of effect
my $var=join(' ',split('','CONFIDENTIAL'));
I rebuilt Perl into a shared library version to link it into Pg.