First of all, huge congratulations to Mat Marquis, Jason Grigsby, Scott Jehl, Ethan Marcotte, Florian Rioval and all the other web geniuses who are working to make responsive images much, much easier for those working with responsive web design.
Today is a milestone. The Responsive Images Community Group of the W3C has now published their proposal for responsive images, the picture element, as a W3C draft. Make sure to read the draft of the picture element. It’s a great step towards a better web.