[Jtsummers]

I'm not underestimating anything because I'm not suggesting producing a formal model of arbitrary, nontrivial systems. My critical point is: Design your system before committing any code to the end result [0]. Formal methods and models are one tool in your designer's kit.

[0] This statement should be qualified with: Especially if it's at all novel to you, your team, your organization, or the world. And the amount of time to spend varies based on its true novelty. A team that's made hundreds of RoR sites can churn a new one out in a week with minimal upfront design effort. A team that's making the next RoR should probably spend more time thinking about what that means before making, or committing code to, it.