I have been playing around with the idea of creating a Drupal 7 theme which should be based on the thoughts responsive web design. So far I'm only working on the html mockup of the design, this is still a alpha version of it and it still needs a lot of work and testing before it is ready to be converted into a Drupal theme.
My first idea is based on the 12 column fixed grid where the site basically just switch down in size and focus when resizing the browser window, when it hits the lower barrier it just excludes the grid layout and keeping foces on the relevant content gets as high a priority as needed.
You can see an alpha demo here.
Future down the road the idea is to allow for the user to decide the priority of the different regions or perhaps even blocks, meaning that the entire layout will be dynamic based on the choices that the user makes.