@meme: Nah. I can't take any credit for this idea.
I get it from here:
https://www.mobileread.com/forums/showthread.php?t=46082
I'm mostly scifi reader, so dividing books into genres is a bit useless. I work with themes instead: (or sub-genres? I'm unsure where the line is drawn) Urban fantasy, Dystopia, Hard/Light sci fi, Alternate history... and so on.
I have this habit to get back to books I've read already. There are some specific tags which help me to navigate myself according to my current mood: Dark theme, Sense of wonder included, Disappointing ending... you get it.
Also, I have books in different languages and finally - I'd like to preserve my own ratings.
I've read e-books on my iPod Touch before and Kindle seemed like almost inevitable evolution. Don't get me wrong - it's great to read on it. But I find annoying to not being able to use it as a portable personal library. After all the device is designed for it.
Calibre can fetch annotations from Kindle (I didn't try yet) but not vice versa (I didn't find how). If you'd be able to make it somehow, I'm sure many readers will thank you in awe!