Best Buy has bought a shelf label system from a company called Pricer, and deployed labels in the 2″ and 4.2″ size. The larger sizes uses a 3-color Spectra E-ink screen (red, black and white), but I can’t say for sure whether the smaller shelf labels uses that screen or just a regular E-ink screen.
One thing I can tell you is that the screens are not as high of a resolution as on your Kindle; the smaller text on the 4.2″ screen was almost illegible due to fuzziness.
But even so, it was pretty cool to see digital shelf labels in widespread adoption. I had almost give up hope of seeing them in the stores I visit. Honestly, despite the obvious advantages (reduced labor, faster turnaround, etc) for a while there it had seemed like retailers had decided to pass on the tech.