While writing Rails apps, I've written several variants on the 'give me an ActiveRecord instance that can't talk to the DB' theme over the last couple of years while writing tests or specs for an app. The basic pattern is a pretty good one - it guarantees you a certain degree of test isolation for your unit tests or specs, when you need it. And, because you're make specific instances isolated, you can get to the DB if you need to.
Something I found myself wrestling with a lot towards the end of my time at the BBC, and something I've been thinking a lot about since, is the deployment of entire servers, not just the deployment of software onto servers. I've spent nearly ten years working with Linux distributions and their OS package management systems, primarily Red Hat and Debian-based systems (Ubuntu, lately). I've also spent a lot of time working with Python and Ruby's OS-independent packaging systems (Distutils, a tiny bit of Setuptools, and Rubygems).