I agree that it'll be a loss for consumers if the Nook disappears. However...
I've owned (or currently own) three Kindles, one Nook (the glow light version), and the new Kobo that got slashvertised here a few weeks ago. As I've posted before, Amazon simply has the best platform of the three (I haven't tried others). It's ridiculously easy to sideload books wirelessly, without jailbreaking, to all of your Kindles at once. More importantly, Kindle will sync the location of sideloaded books. Third-party publishers, such as Baen, already offer MOBI files, so you don't even need to use Calibre.
The only other eBook vendor I know of that syncs sideloaded stuff is Apple, and they don't have a dedicated eReader, and sideloading is a little bit trickier than the Kindle. I haven't checked out Google; how are they in this arena?
I've also found Amazon to be the cheapest, at least for books I actually want to read. Two books on my shortlist, A Fire Upon the Deep and The Last Colony, are both $2 more on the Kobo store. A couple dollars here and there add up. (My solution right now is to buy on Amazon and convert it for the Kobo.)
What makes it all so frustrating is that Amazon has the worst hardware of the three. It isn't that it's bad, it's that it's very utilitarian. The Nook has the best-feeling reader, while the Kobo has the best software (their text options are downright great), screen, and backlight.