It depends. At work among developers, we use a local directory with different paths for different systems and architectures
in reply to How Do You Manage Your Perl Modules?
etc. Each computer knows where to search for its libraries, and there is a special cpan wrapper that can install a package for all the combinations.
For shipping one application, we use darkpan on Linux, but cpan on Windows (Strawberry, previously PPM with ActiveState).
And so on.