Whitney summarizes Jason Fried's talk on 37Signals design and development process. They go straight from sketch to prototype, and iterate the prototype until it is ready to launch.

One of the few articles I've found useful from these guys recently: a cluttered interface is actually the most useful in this case study, since speed is more important than clarity and the users can be expected to learn it over time.

rd. You can’t help but know your way around Photoshop after working in it for 10 years, but I still find it awkward to get simple things done. Working with a pen feels so much more natural to me than going back

So, to add into the fray, here’s my thoughts on using personas... If you’re just going to guess on the personas, why bother? Just design for yourself, like the 37Signals team does.However, when you do the field studies, you create relationships with the people in your research. The persona becomes a package for containing what you’ve learned from your field research. A package that is transportable to everyone on the team, so they can have the same benefits of knowing the users as you have.