Marco Arment has published a great comparison between the Nook Simple Touch and the Kindle 3. This bit near the end sums up his thoughts quite nicely:

My ideal e-reader would be the Nook hardware and interface, but backed by the Kindle’s ecosystem and services. It’s easier for Amazon to achieve Nook-like hardware design than for B&N to achieve a Kindle-like ecosystem, so it’s much more likely that the next Kindle will be a better fit than the current (or next) Nook.

I currently own a Kindle 2 and even though a lot of the features in these newer readers are nice, I don’t expect I’ll be buying one, even in the next couple of years. I openly admit that I don’t read books all that often. But, I do read more than anyone I know. Tools like Fever and Marco’s Instapaper make it super easy to read, a lot. But, I have a feeling that ebook readers aren’t the type of devices that users will upgrade very often. I think Amazon and Barnes & Noble need to assume that their customers are only going to upgrade once every three years or so.

People that read, read a lot. But, there isn’t a lot you can add to an ebook reader that will make people feel the need to upgrade.