[rimantas]

Unless I am missing something the title is wrong. CSS Sprite means that there are several images in single image file. This is just Data URI encoded images, not sprites. IIRC google used similar technique for the previews of pages in SERPs.

[T-R]

They're sending the Data URIs in a single JSON file, so it gives the same benefit (fewer HTTP requests) as normal CSS sprites. When you just combine multiple images into one (as you do for normal CSS sprites) you lose the information on the size/location of each sprite. An array of Data URIs keeps the images separate, so you don't need to put size/location information into CSS/Javascript/HTML.