Lars Strojny has posted the second part of his look at dependency injection and the refactoring it makes possible. If you'd like to start from the beginning, you can read about part one here.

He breaks it up into two sections (really three, but he advises to ignore the third):

Introducing a parameter in to the dependency injection container's configuration
• Setting it up to allow for checks against the environment (development, production, etc)

Code samples and example XML configurations are included for both points to help make them clearer.