I'll put it in a nutshell to save those who have busy schedules can skip some reading. The Nook UI is prettier. The Kindle UI is faster.
Ok, the busy folks have left the stadium. Here's the more detailed play-by-play (I'm beating the sports metaphors to death. Well, it's either that or watch the Olympic curling this afternoon).
I'm talking about the Kindle 2, of course, which is faster than the first Kindle. Not that it's terribly fast: the refresh rate of e-ink screens is a bit slow under the best of conditions. However, in my experience, page turns on the Kindle are approximately twice as fast as the Nook. Selecting text to highlight is simply painful on the Nook, and much better on the Kindle. If you're the type of person who likes to highlight their books, get the Kindle.
Highlighting text on the Nook is a fiddly exercise in using the touchscreen to move the pointer on the reading screen; waiting, waiting for the pointer to react; then repeating. Finally, you'll get a chance to enter text on a touchscreen interface, and tap "submit." The whole thing is an exercise in Buddhist patience. The one part of this exercise where the Nook exceeds the Kindle is the keyboard; the Kindle keyboard is not made for speed typing. You can take notes on the Kindle, but they will be more like tweets than paragraphs. However, in every other respect, annotating on the Kindle is better. It's faster, and your annotations are saved in a form that is quite a bit more useful.
On the Kindle, your bookmarks and notes are saved in a list in which the actual text of the bookmark or note (or a portion of it), appears on the screen; by moving the cursor and pressing the 5-way navigation button, you can go directly to the highlighted text, or see the whole note. On the Nook, however, all you see is a list of page numbers that you have bookmarked. You have to go to each page to see it; there is no context given. Combined with the overall slowness of the communication between the LCD screen and the reading screen, this makes bookmarks and notes more difficult to use than beneficial to the reading experience. In fact, in some books, there is only given the option to "view notes on this page," with no apparent way whatsoever to find all the notes one may have made -- other than paging slowly through the book. In short, the Nook is best for people who just like to read straight through and do not annotate as they read. Annotators and note-takers--get the Kindle.
Finally, a word needs to be said about consistency. Consistent UIs are always easier to learn and to use. The Kindle's UI is consistent throughout, if not fancy. The Nook is oddly inconsistent. Sometimes you back out of your menus on the LCD screen using a back arrow. At other times, you tap an "X" to close a menu. The result is, of course, that it is easy to forget where you are in the menus and accidentally close the book you are reading, which is annoying.
The communication between the LCD screen and the reading screen is quite slow. Otherwise, the idea is good, and one finds oneself wishing that both Amazon and Barnes and Noble had a spy in each other's training camp. The Kindle interface could use a little more pizzazz, and the Nook interface could use more speed and consistency, and handle annotating better.






