Boxes and Arrows has just published a new article by Trevor van Gorp called Design for Emotion and Flow that delves farther into how to apply the theory of flow to web design:
Remember, designing for flow doesn't require a new set of tools or skills - only a different way of thinking. Finding the right balance of design and challenge can help focus attention and create flow, which results in immersive and engaging user experiences.
I found the section on "Goal-directed vs. Experiential Use" especially interesting.
