Bart gives a presentation on responsive design and lessons learned from building the Rock Werchter website. The key lessons are to think of content first and design around it, design for specific breakpoints to ensure things work at different sizes, start with a mobile-first approach prioritizing touch navigation and information architecture, focus on conversion goals like making the "buy tickets" button prominent, build for high resolution retina displays from the start, and use responsive images and back-end to automatically scale and serve the right image sizes. The overall message is that responsive design requires considering content, design, users and business goals at each step to create a high quality experience across devices.