Very cool stuff... the transitions bother me a little. I'm of a notion that animation should be handled by js while (cross-browser) design should be strictly in the css. Fantastic stuff to use for personal projects, tho, if you really really want to avoid js at all costs.
Designing for responsive websites can be a bit challenging at first because the process is so different. As designers, we've gotten used to building pixel-perfect mockups as our web blueprints. But responsive design takes a different approach.
"Because so much of a layout can be created with CSS it may feel like your role as a designer has diminished. Really, your role has just changed. Web design for too long has been about designing the interface while neglecting the content.
The layout is still important but the developer can do much of it. The designer should focus on making sure the goals of the website are met. Spend the most time on strengthening the conversion process, emphasising important content, and making it more palatable and digestible."