I love eInk, but after reading the entire "A Song of Ice and Fire" series (all 5000+ pages) on my iPod Touch using the Kindle app, I think the right form factor and good software make a big difference.
Little-known fact: the Nook Color (vastly) outsells the e-ink Nook.
I was surprised too.
Maybe people who want e-ink just buy a Kindle.
Or maybe people who want e-ink are a single-digit percentage of the market.
If a consumer does research, as I did, and looks for comparison of the eInk of the Nook and of the Kindle, you quickly discover side by side photos of the Nook and Kindle and conclude that the Kindle eInk is better (it does use a more current version of eInk than the Nook after all). If you wanted color - you with w/ the Nook because that was the option you had out of the big two, otherwise, with the Kindle.
eInk isn't the best solution in a lot of instances. A back-lit display is a lot more visually accessible.