[EDIT: The presentation doesn't appear to work on mobile devices. I'm trying deck.js, and I'm not sure I like it.]
When I started my current job, I was introduced to the custom Dependency Injection framework they built. At the time, I was dismissive: "It's programming via config file, which is always limiting (and so, a Bad Idea)." "It's something that Java needs, but not Perl."
Slowly, and with great reluctance, I learned where dependency injection fits into a large framework: It removes the work of creating objects. Any object. Anywhere.
For an idea of how powerful this is, do a quick search through your libraries and scripts (except for tests) for /->new/. Hopefully, the results will only be defaults (otherwise you've got tight coupling, another problem DI can fix). But every time you call an object constructor is another place where dependency injection can reduce the amount of code you write and maintain.
So, since the bureaucracy means I can't simply open-source the DI framework we have at $dayjob, I decided to make my own.