I just finished updating CPAN::Mini::Inject to fix a bug with dirmode settings. The dirmode would be set correctly during CPAN::Mini's mirroring process, but any files that CPAN::Mini::Inject added or created did not have the correct mode set. This made doing updates in a multi-developer environment difficult.
A little background into CPAN::Mini::Inject. I work on a number of projects where the modules I write can not be released onto CPAN. When working in a single server environment this isn't much of an issue, but my current project involves 4 different servers. Managing 15 private modules on each of these servers was becoming difficult. We use CPANPLUS on each server to manage publicly available modules, with CPAN::Mini::Inject we can now use CPANPLUS for our private modules as well.
As it's name suggests, CPAN::Mini::Inject allows you to add (inject) your own private modules into a CPAN::Mini mirror. Allowing the use of CPAN/CPANPLUS to install public and private modules with one procedure.
We also use a separate CPAN::Mini::Inject mirror to test the installation of our development modules before releasing. This ensures that during the process any prerequisites are installed, and that all tests pass.