“ You don't need to re-install perl, the built-in one works just fine ... ”

No one suggested re-installing Perl but to create a second install for development purposes :-) Working with the system Perl can be fine until it isn't and then it's a huge headache (e.g., Installing modules and plugins to included modules in the same location). This became more true with Snow Leopard and has been documented, among other places, here: How Do You Use Manage Perl Modules When Using A Package Manager, here: Perl Strategy For A New Snow Leopard User and here: Perl Script Problems

* Some of these problems were due to Snow Leopard's 32-bit/64-bit issues which should no longer exist in Lion

UPDATE
Same Day, 13.Jan.2012 :: 2:10 PM ::	Added other links discussing maintaining separate Perl builds on Mac OSX and note on 32-bit/64-bit (Snow Leopard).