Designing for retina

After responsive design, the next challenge is awaiting us: designing for retina displays. The blogosphere is starting to post some interesting articles. I particularly liked this first thoughts by a graphic designer. Which led me to retina.js (drupal sandbox here). Another helpful tool is this flowchart howto retinafy your website. Also the responsive images drupal module offers retina support in their latest dev. But I'm not sure yet how it compares to retina.js.