I live in Canada (or more accurately outside of the United States) so the Nook isn't an option. I am not deigned worthy enough to buy it due to my residency on "foreign" soil.
The above is only partly tongue-in-cheek. What sets the Kindle 2 apart from all other readers is that it is sold to many countries and is designed to work wirelessly in 200 countries. That's as global as you can get. If you find a title you like at Amazon, seconds later you can be reading it wherever you are.
This is a non-trivial advantage.
Plus, hands up anyone who thinks Amazon does NOT have the best chance of being here five years from now -- including holding a copy of your backup library of e-books: Amazon, Border, Barnes & Noble, Waterstones, WHSmith, Redgroup, Chapters/Indigo, Sony e-book Store ... etc etc. It's a red herring to say Amazon is a "closed format" when suggesting, for example, Sony is an open one? DRM is DRM: it can be overcome if necessary and, more to the point, if the vendor is still there, it hardly matters.
Plus, as the last post pointed out, you are not "locked in" to Amazon with a Kindle -- lots of vendors offer non-DRM books that open perfectly well on a Kindle.
It's worth a reminder: Apple built iTunes on the closed AAC format when the rest of the world fell in love with mp3. Apple not only abandoned DRM AAC, it now sells DRM-free mp3. And it remains the market leader for music content. Why? Because they sorted out the DRM issue AND provided the very best online experience for purchasing, managing and consuming music content.
Of all the vendors selling e-books today, which has the richest content, and content management system, for consuming e-books? If you answer "Amazon", as I do, you'll see why the Kindle is a very good choice.
One more thing: only Amazon has made a serious effort to enhance the end user experience of a device you have already bought. The Kindle 2 has been upgraded with longer battery life, faster page turns, international accessibility, additional formats, and soon social networking and further font, book management and other tweaks. All in the past eight months: Amazon is truly committed to the platform. Can Sony or any other vendor say prove the same claim?