This post was originally written in January 2009.
Continuing the free ebook spree, I’ve found 3 more on creativity and design.

One of the principles of lean startups is ferocious customer-centric rapid iteration. To validate assumptions, data must be collected from users interacting with the product, a fact frequently forgotten by opinionated developers.
Here are two good presentations about metrics, one about business metrics for startups, and other specifically about web applications design metrics.