What about optimizing your app later? I've rolled out a number of rails apps, and I now feel that the rapid prototyping it provides is actually a form of technical debt. The execution speed and memory footprint mean you will have to scale harder, faster. I would like to remove framework components and middleware that I am not actually using, and transition cleanly from a rapid rollout to an optimized final product. But even in rails 3 I haven't seen good evidence that it's possible to do this, without being hackish. How do Django and other frameworks handle this?

Another way of saying it is I would like a framework that is "additive," where you start with a very lightweight core and then add components as you need them.