There has been a lot of buzz in the website world regarding responsive layout over the last year or so; and really gaining steam in the last 6 months. Being heavily involved with WordPress and continually researching themes and plugins as they are introduced, I have witnessed a huge demand for responsive WordPress themes.
Responsive layout is a way to design websites so that they are optimized for all portal sizes; desktop, tablet, mobile and everything in-between. This can be as simple as scaling everything (images, text, etc.) down for a mobile site or even displaying completely different content based on device.
With proper consideration of your content and users, responsive design promises to be the future of web design. Now you can add content to one website to have it available on any device. Of course there is still some maturing that needs to happen before this technology can be effectively used in all industries, but we aren't that far off.