Joel Spolsky - Seattle:

"If you ever started a new project by writing code, and you thought you’d “design as you went along,” what you’re doing is driving around with the handbrakes on. Here’s why. Designing a feature by writing a thoughtful spec takes about 1/10th as much time as writing the code for that feature—or less. If you try to code as you design, then you’re interrupting your short spurts of design with long spurts of coding."