Maciej Cieglowski describes what happened once Yahoo! let it slip they were thinking of shutting down Delicious, and thousands of users all started moving to his competing service Pinboard all at once.
Pinboard is a PHP app that Maciej describes as "a thin wrapper around some carefully tuned database queries", a design that's an intentional response to how we do things in Ruby/Rails. And my favorite bit in this post is how he describes how we do things in Rails:
It has become accepted practice in web app development to design in layers of application caching from the outset. This is especially true in the world of Rails and other frameworks, where there is a tendency to treat one's app like a high-level character in a role-playing game, equipping it with epic gems, sinatras, capistranos, and other mithril armor into a mighty "application stack".
It's funny because it's true. Plus, "epic sinatras" is now my phrase of the day.