I have a (possibly) unique perspective on this question...
I am a loyal Amazon customer, and have been since the very first days of Prime membership (back in 2006). As a loyal Amazon customer, and Kindle afficianado, I got a Kindle Fire on the very first day they were released. I have used it every day since then. I have loved the 7" size, and the integration of books, music, movies, and apps.
Having said all of that, I have to admit that I just sold my Fire and preordered the 16GB N7. Here's why: The Kindle for android app will allow me to read all of my books just like on the Fire. The Amazon MP3 app will let me listen to all my music, just like on the Fire. But the N7 has twice the processor, twice the RAM, twice the ROM, bluetooth, and access to the entire Android marketplace. Plus, you can still access the Amazon app store if you really want to.
The only thing you can't do is watch Amazon Instant Video. This is really going to suck for me, because I have bought a lot of movies and TV shows on Amazon, and really enjoyed downloading them to the Fire to watch offline. Still, I decided to go with the N7 because all of the other benefits outweighed the loss of AIV.
The only possible spoiler would be the Kindle Fire 2 which is probably going to be announced at the end of the month.