Link parkin’: Luke Wroblewski describes how Bagcheck practices progressive enhancement by developing the product starting from the web API, then constructing command line interface (CLI) tools, and thence to client side interfaces.
From a UNIX perspective, I’ve noticed a CLI is really helpful because you can smoothly tie into standard UNIX scripting tools. This allows for large scale automation which you need more often than not.
Bonus links: The Bagcheck technology stack and Wroblewski’s writings which often include comprehensive notes on interesting conference sessions.