Legendary computer scientist Donald Knuth wrote that "premature optimization is the root of all evil," referring to the amount of time and effort programmers spend optimizing non-critical elements of their applications.

On the other hand, as pointed out in this blog post by Metamarket CTO Mike Driscoll on the company's migration to Node.js, it's better to swap out critical infrastructure early in a startup's life.

So, when you're building an application - when do you start thinking about scalability?